Exhibit 99.1

HOUGHTON MIFFLIN HARCOURT ANNOUNCES THIRD QUARTER 2018 RESULTS

Reaffirms 2018 outlook, on track for approval in 2019 adoptions

BOSTON – November 8, 2018 – Global learning company Houghton Mifflin Harcourt (“HMH” or the “Company”) (Nasdaq: HMHC) today announced its operating and financial results for the third quarter ended September 30, 2018.

Operating Highlights:

“We had a solid third quarter, delivering billings growth of 1.5% driven by strength in Extensions and Trade, which demonstrates the merits of our strategy,” said Jack Lynch, President and Chief Executive Officer of HMH. “We remain focused on executing against our long-term strategy, and believe we are well positioned for the large adoption opportunities in 2019.”

Joe Abbott, Chief Financial Officer of HMH added, “We remain on track to deliver against the targets we set at the start of the year, adjusted for the Riverside divestiture, and have reaffirmed our fiscal year 2018 outlook. We are nearing completion of our restructuring program and remain focused on execution as we close out the year and look ahead to a larger market opportunity in 2019.”

Third Quarter 2018 Financial Results:

Net Sales: HMH reported net sales of $516 million for the third quarter of 2018, a slight increase compared to the same quarter of 2017. The net sales increase was driven by a $15 million increase in our Trade Publishing segment offset by a $15 million decrease in our Education segment. Within our Trade Publishing segment, the increase was primarily due to licensing income driven by a new agreement pertaining to our classic backlist titles 1984 and Animal Farm. Within our Education

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segment, the decrease was primarily due to lower net sales from Core Solutions, which declined by $34 million from $277 million in 2017 to $243 million. The decrease was primarily due to decreases in sales relating to disciplines reaching the end of their product lifecycle that are scheduled to be replaced next year with newer programs. Partially offsetting the decrease in our Core Solutions sales was an increase in sales from our Extensions businesses, which primarily consist of our Heinemann brand, intervention, and supplemental products as well as professional services. Extensions businesses net sales for the current period increased $19 million to $207 million in 2018 primarily driven by higher Heinemann net sales. The primary driver of the increase in our Heinemann net sales was sales of the Fountas & Pinnell Classroom product, which benefited from additional product launches during the quarter.

Billings: HMH reported billings of $571 million for the third quarter of 2018, up $8 million from the same quarter of 2017. Education and Trade Publishing segment billings for the third quarter of 2018 were $504 million and $67 million, respectively, compared with $512 million and $50 million, respectively, for the same periods in 2017. Our Trade Publishing segment billings increase of $17 million was due to licensing income driven by a new agreement pertaining to our classic backlist titles 1984 and Animal Farm. Within our Education segment, the $8 million decline in billings was attributed to a decrease in billings from Core Solutions, which declined by $25 million from $299 million in 2017 to $274 million. The primary driver of the decrease in Core Solutions billings were decreases in billings relating to disciplines reaching the end of their product lifecycle that are scheduled to be replaced next year with newer programs. Billings within our science discipline, which is a new program, increased year over year offsetting some of the older program declines along with a large order from Puerto Rico. Partially offsetting the Core Solutions billings decline was an increase in billings from our Extensions businesses of $16 million to $230 million in 2018, primarily driven by higher Heinemann billings. The primary driver of the increase in our Heinemann billings was billings of the Fountas & Pinnell Classroom product, which benefited from additional product launches during the quarter.

Cost of Sales: Overall cost of sales decreased 3%, or $7 million, to $238 million in the third quarter of 2018 from $245 million in the same period of 2017, primarily due to a $7 million reduction in publishing rights and pre-publication amortization.

Selling and Administrative Costs: Selling and administrative costs increased $3 million to $176 million for the third quarter of 2018 from the same period of 2017, primarily due to variable expenses such as commissions attributable to the Heinemann billings, and depository fees which is driven by geographic sales mix.

Operating Income: Operating income for the third quarter of 2018 was $92 million, a $3 million improvement from the same period of 2017 primarily due to aforementioned changes in cost of sales.

Net Income: Net income of $86 million in the third quarter of 2018 was $4 million, or 5%, lower compared to a net income of $91 million in the same quarter of 2017. Net income from continuing operations in the third quarter was $84 million, a $5 million decrease from the $89 million in the same quarter of 2017, due primarily to the same factors impacting operating income and an unfavorable change in our tax provision of $6 million, from a benefit of $10 million for the same period in 2017 to a benefit of $4 million in 2018. The reduction in benefit was primarily due to the Tax Cuts and Jobs Act of 2017 (“2017 Tax Act”) resulting in a lower annual effective tax rate and our ability to utilize indefinite-lived deferred tax liabilities as a source of future taxable income in our assessment of realization of deferred tax assets. Income from discontinued operations, net of tax, increased by $1 million to $2 million from the same period in 2017.

Adjusted EBITDA from continuing operations: Adjusted EBITDA from continuing operations for the third quarter of 2018 was $160 million, a $1 million unfavorable change from $161 million in the same quarter of 2017, primarily due to the aforementioned changes in selling and administrative costs.

Nine Months Ended September 30, 2018 Financial Results:

Net Sales: HMH reported net sales of $1,073 million for the first nine months of 2018, down $20 million from the same period of 2017. The net sales decrease was driven by a $29 million decrease in our Education segment, offset by a $9 million increase in our Trade Publishing segment. Within our Education segment, the decrease was primarily due to lower net sales from Core Solutions, which declined by $63 million from $519 million in 2017 to $456 million. The primary drivers of the decrease in Core Solutions sales were decreases in sales to disciplines reaching the end of their product lifecycle that are scheduled to be replaced next year with newer programs. Net sales within our science discipline, which is a new program, increased year over year offsetting some of the older program declines. Also contributing to the decline in Core Solutions was the non-recurrence of the $5.0 million one-time fee we recognized in 2017 in connection with the expiration of a distribution agreement. Partially offsetting the decrease in our Core Solutions sales was an increase in sales from our Extensions businesses of $34 million from $444 million in 2017 to $478 million in 2018 primarily driven by higher Heinemann net sales largely attributed to the Fountas & Pinnell Classroom product, which was introduced in the third quarter of 2017, and additional product launches during the third quarter of 2018. Within our Trade Publishing segment, the increase was primarily due to licensing income driven by a new agreement pertaining to our classic backlist titles 1984 and Animal Farm. The increase was partially offset by a decrease in ebook sales.

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Billings: HMH reported billings of $1,108 million for the first nine months of 2018, a slight decline compared to the same period of 2017. Education and Trade Publishing segment billings for the first nine months of 2018 were $967 million and $141 million, respectively, compared with $979 million and $129 million, respectively, for the same periods in 2017. The billings decrease was driven by our Education segment, which declined by $12 million from 2017 to $967 million. The primary drivers of the decrease in our Education segment was Core Solutions, which declined by $55 million. The decrease in Core Solutions billings was due to decreases in billings to disciplines reaching the end of their product lifecycle that are scheduled to be replaced next year with newer programs. Billings within our science discipline, which is a new program, increased year over year offsetting some of the older program declines along with a large order from Puerto Rico. Also contributing to the decline in Core Solutions was the non-recurrence of the $5 million one-time fee we recognized in 2017 in connection with the expiration of a distribution agreement. Offsetting the decrease in billings in Core Solutions was an increase in our Extensions businesses. Extensions businesses billings for the current period increased $43 million from $449 million in 2017 to $492 million in 2018 primarily driven by higher Heinemann billings of the Fountas & Pinnell Classroom product, which was introduced in the third quarter of 2017, and additional product launches during the third quarter of 2018. In the first nine months, HMH’s share of the addressable portion of the AAP market declined by two points. Within our Trade Publishing segment, there was a billings increase of $11 million which was due to licensing income driven by a new agreement pertaining to our classic backlist titles 1984 and Animal Farm.

Cost of Sales: Overall cost of sales decreased 4%, or $25 million, to $568 million in the first nine months of 2018 from $593 million in the same period of 2017, primarily due to lower volume in 2018 coupled with a $15 million reduction in publishing rights and pre-publication amortization.

Selling and Administrative Costs: Selling and administrative costs increased by $4 million for the first nine months of 2018 due higher depreciation expense of $3 million as a result of our increased investment in business systems and infrastructure; an increase in professional fees of $3 million in 2018 which related to a $5 million non-recurring insurance reimbursement received in 2017; an increase in discretionary costs of $2 million related to travel and entertainment, promotion and an increase in commissions and depository fees of $3 million. Offsetting the increase in selling and administrative costs was lower IT expenses of $4 million relating to maintenance contracts, hardware and telecommunications. Further, there were lower net labor costs and other fixed costs due to actions taken under the 2017 Restructuring Plan partially offset by higher employee benefit and medical expenses as well as planned merit increases.

Operating Loss: Operating loss for the first nine months of 2018 was $16 million, a $30 million improvement from the $46 million operating loss recorded in the same period of 2017 primarily due to the $33 million decrease in the charge associated with our 2017 Restructuring Plan, which primarily occurred in 2017, and the reduction in cost of sales partially offset by the aforementioned changes in net sales.

Net Loss: Net loss of $38 million in the first nine months of 2018 was $39 million, or 50%, lower compared to a net loss of $77 million in the same period of 2017. Net loss from continuing operations for the nine months ended, September 30, 2018 was $51 million, a $33 million improvement from the $84 million net loss from continuing operations in the same period of 2017 due primarily to the same factors impacting operating loss and a favorable change in our tax provision of $8 million, from an expense of $10 million for the same period in 2017 to an expense of $2 million in 2018. The reduction in tax expense was primarily due to the 2017 Tax Act resulting in a lower annual effective tax rate and our ability to utilize indefinite-lived deferred tax liabilities as a source of future taxable income in our assessment of realization of deferred tax assets. Also, income from discontinued operations, net of tax increased $6 million to $13 million from $7 million in 2017.

Adjusted EBITDA from continuing operations: Adjusted EBITDA from continuing operations for the first nine months of 2018 was $190 million, a $6 million unfavorable change from $196 million in the same period of 2017, primarily due to the aforementioned changes in net sales.

Cash Flows: Net cash provided by operating activities for 2018 was $43 million compared with $38 million in 2017. The $5 million increase in cash provided by operating activities from 2017 to 2018. Net cash provided by operating activities from continuing operations was $26 million in 2018, a $6 million increase compared to 2017. The increase in net cash provided by operating activities from continuing operations was primarily driven by more profitable operations, net of non-cash items of $6 million. Net cash provided by operating activities included $17 million and $18 million of cash flow from discontinued operations in 2018 and 2017, respectively. HMH’s free cash flow from continuing operations, defined as net cash from operating activities minus capital expenditures, as of September 30, 2018 was a usage of $108 million compared with a usage of $101 million for the same time period in 2017. The primary drivers of the unfavorable change in free cash flow was an increase in capital expenditures related to the timing of pre-publication costs in 2018. As of September 30, 2018, HMH had $134 million of cash and cash equivalents and short-term investments compared to $235 million at December 31, 2017.

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Corporate Initiatives:

HMH continues to implement its ongoing initiatives to improve the Company’s operational efficiency and right-size its cost structure. Organizational design changes, aimed at reducing complexity in the organization, were completed in 2017, and HMH expects to substantially complete the remaining planned actions by the end of 2018. The identified initiatives are expected to result in approximately $70 million to $80 million in annualized cost savings by the end of 2018.

Conference Call:

At 8:30 a.m. ET on Thursday, November 8, 2018, HMH will host a conference call to discuss the results with its investors. The call will be webcast live at ir.hmhco.com. The following information is provided for investors who would like to participate:

Toll Free: (844) 835-6565

International: (484) 653-6719

Passcode: 1959829

Moderator: Brian Shipman, Senior Vice President, Investor Relations

Webcast Link: https://edge.media-server.com/m6/p/4pz5nkcb

An archived webcast with the accompanying slides will be available at ir.hmhco.com for one year for those unable to participate in the live event. An audio replay of this conference call will also be available until November 17, 2018 via the following telephone numbers: (855) 859-2056 in the United States and (404) 537-3406 internationally using passcode 1959829.

Use of Non-GAAP Financial Measures:

To supplement our financial statements presented in accordance with Generally Accepted Accounting Principles (GAAP) and to provide additional insights into our performance (for a completed period and/or on a forward-looking basis), we have presented adjusted EBITDA from continuing operations and free cash flow. These measures are not prepared in accordance with GAAP. This information should be considered as supplemental in nature and should not be considered in isolation or as a substitute for the related financial information prepared in accordance with GAAP. Management believes that the presentation of these non-GAAP measures provides useful information to investors regarding our results of operations and/or our expected results of operations because it assists both investors and management in analyzing and benchmarking the performance and value of our business.

Management believes that the presentation of adjusted EBITDA provides useful information to our investors and management as an indicator of our performance that is not affected by: fluctuations in interest rates or effective tax rates; levels of depreciation or amortization; non-cash charges; fees, expenses or charges relating to acquisition-related activities, including purchase accounting adjustments, integration costs and transaction costs, as well as to securities offering- and debt refinancing-activities; charges associated with restructuring and cost saving initiatives, including severance, separation and facility closure costs; certain legal settlements and awards; and non-routine costs and gains. Accordingly, management believes that this measure is useful for comparing our performance from period to period and makes decisions based on it. In addition, targets in adjusted EBITDA (further adjusted to include the change in deferred revenue) are used as performance measures to determine certain incentive compensation of management. Management believes that the presentation of free cash flow provides useful information to our investors because management regularly reviews free cash flow as an important indicator of how much cash is generated by general business operations, excluding capital expenditures, and makes decisions based on it.

Other companies may define these non-GAAP measures differently and, as a result, our use of these non-GAAP measures may not be directly comparable to adjusted EBITDA and free cash flow used by other companies. Although we use these non-GAAP measures as financial measures to assess our business, the use of non-GAAP measures is limited as they include and/or do not include certain items not included and/or included in the most directly comparable GAAP measure. Adjusted EBITDA should be considered in addition to, and not as a substitute for, net income or loss prepared in accordance with GAAP as a measure of performance; and free cash flow should be considered in addition to, and not as a substitute for, net cash provided by operating activities prepared in accordance with GAAP. Adjusted EBITDA is not intended to be a measure of liquidity nor is free cash flow intended to be a measure of residual cash flow available for discretionary use. You are cautioned not to place undue reliance on these non-GAAP measures. A reconciliation of these non-GAAP financial measures to the most directly comparable GAAP financial measures (to the extent available without unreasonable efforts) and related disclosure is provided in the appendix to this news release.

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About Houghton Mifflin Harcourt

Houghton Mifflin Harcourt (Nasdaq: HMHC) is a global learning company committed to delivering integrated solutions that engage learners, empower educators and improve student outcomes. As a leading provider of K–12 core curriculum, supplemental and intervention solutions and professional learning services, HMH partners with educators and school districts to uncover solutions that unlock students’ potential and extend teachers’ capabilities. HMH serves more than 50 million students and 3 million educators in 150 countries, while its award-winning children’s books, novels, non-fiction, and reference titles are enjoyed by readers throughout the world. For more information, visit www.hmhco.com

Follow HMH on Twitter, Facebook and YouTube.

Contact

Investors

Brian S. Shipman, CFA

Senior Vice President, Investor Relations

(212) 592-1177

brian.shipman@hmhco.com

Media

Bianca Olson

SVP, Corporate Affairs

617-351-3841

bianca.olson@hmhco.com

Forward-Looking Statements:

The statements contained herein include forward-looking statements, which involve risks and uncertainties. These forward-looking statements can be identified by the use of forward-looking terminology, including the terms “believes,” “estimates,” “projects,” “anticipates,” “expects,” “could,” “intends,” “may,” “will,” “should,” “forecast,” “intend,” “plan,” “potential,” “project,” “target” or, in each case, their negative, or other variations or comparable terminology. Forward-looking statements include all statements that are not statements of historical facts. They include statements regarding our intentions, beliefs or current expectations concerning, among other things, our results of operations, including billings and net sales; financial performance, financial condition; liquidity; products and services, including for new adoptions; outlook for full year 2018; prospects; growth; markets and our positions therein; strategies, including with respect to investing in our Core Solutions and Extensions businesses and operational excellence; efficiency and cost savings initiatives, including actions thereunder and expected impact and timing; the industry in which we operate; and potential business decisions. We derive many of our forward-looking statements from our operating budgets and forecasts, which are based upon many detailed assumptions. We caution that it is very difficult to predict the impact of known factors, and, of course, it is impossible for us to anticipate all factors that could affect our actual results. All forward-looking statements are based upon information available to us on the date hereof.

By their nature, forward-looking statements involve risks and uncertainties because they relate to events and depend on circumstances that may or may not occur in the future. We caution you that forward-looking statements are not guarantees of future performance and that our actual results may differ materially from those made in or suggested by the forward-looking statements contained herein. In addition, even if our results are consistent with the forward-looking statements contained herein, those results or developments may not be indicative of results or developments in subsequent periods.

Important factors that could cause our results to vary from expectations include, but are not limited to: changes in state and local education funding and/or related programs, legislation and procurement processes; changes in state academic standards; state acceptance of submitted programs and participation rates therefor; industry cycles and trends; the rate and state of technological change; state requirements related to digital instruction; changes in product distribution channels and concentration of retailer power; changes in our competitive environment, including free and low cost open educational resources; periods of operating and net losses; our ability to enforce our intellectual property and proprietary rights; risks based on information technology systems and potential breaches of those systems; dependence on a small number of print and paper vendors; third-party software and technology development; possible defects in digital products; our ability to

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identify, complete, or achieve the expected benefits of, acquisitions; unanticipated consequences of the recently completed disposition of our Riverside clinical and standardized testing business; our ability to execute on our long-term growth strategy; increases in our operating costs; exposure to litigation; major disasters or other external threats; contingent liabilities; risks related to our indebtedness; future impairment charges; changes in school district payment practices; a potential increase in the portion of our sales coming from digital sales; risks related to doing business abroad; changes in tax law or interpretations; management and other personnel changes; timing, higher costs and unintended consequences of our operational efficiency and cost-reduction initiatives; and other factors discussed in the “Risk Factors” section of our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and other news releases we issue and filings we make with the SEC. In light of these risks, uncertainties and assumptions, the forward-looking events described herein may not occur.

We undertake no obligation, and do not expect, to publicly update or publicly revise any forward-looking statement, whether as a result of new information, future events or otherwise, except as required by law. All subsequent written and oral forward-looking statements attributable to us or to persons acting on our behalf are expressly qualified in their entirety by the cautionary statements contained herein.

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Houghton Mifflin Harcourt Company

Consolidated Balance Sheets

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Houghton Mifflin Harcourt Company

Consolidated Statements of Operations

(Unaudited)

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Houghton Mifflin Harcourt Company

Consolidated Statements of Cash Flows

(Unaudited)

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Houghton Mifflin Harcourt Company

Non-GAAP Reconciliations (Unaudited)

Adjusted EBITDA ¹

Consolidated

(in thousands of dollars)

Free Cash Flow ¹

Consolidated

(in thousands of dollars)

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Houghton Mifflin Harcourt Company

Calculation of Billings (Unaudited)

Billings ¹ (in thousands of dollars)

Consolidated ¹

Education ¹

Trade Publishing ¹

Billings is an operating measure utilized by the company derived as shown above.

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