What: Shares of Chegg (CHGG 1.06%) were down 39% as of 11:30 a.m. EST Tuesday after the online education specialist reported mixed fourth-quarter 2015 results and a disappointing forward outlook.

So what: Quarterly revenue fell 19% year over year to $68.2 million, including 32% growth in Chegg Services revenue to $28.7 million, 33.7% growth in Digital revenue to $38.1 million, and a 46.2% decline in Print revenue, to $30.1 million. Based on generally accepted accounting principles (GAAP), that translated to net income of $3.6 million, or $0.04 per share, up from $0.02 per share in the same year-ago period. On an adjusted (non-GAAP) basis, net income fell 19.7% to $13.2 million, or $0.14 per share. Adjusted earnings before interest, taxes, depreciation, and amortization (EBITDA) fell 18.7% year over year to $15.3 million.

Analysts, on average, were anticipating lower adjusted net income of $0.12 per share, but on higher revenue of $72.1 million.

Chegg CEO Dan Rosenswieg, noted that Chegg Study enjoyed particularly strong growth, leading to new company high marks for subscribers, renewal, and engagement. "Driven by our higher margin Chegg Services," Rosenswieg elaborated, "we also delivered our first full year of non-GAAP profitability, and we are beginning to see the leverage in our student-centric business model. In the final year of our transition to a commission-based textbook model, an important nuance to understand is that, as previously announced, total GAAP revenue declines in 2016, while we expect profitability to materially improve."

Now what: For the current quarter Chegg anticipates total GAAP revenue of $60 million to $65 million, pro forma revenue of $44 million to $47 million, Chegg Services revenue of $24 million to $26 million, and an adjusted EBITDSA loss in the range of $2 million to roughly breakeven. Analysts, for their part, were anticipating significantly higher GAAP revenue of $72.1 million.

For perspective, pro forma revenue adds perspective by assuming Chegg would have already transitioned to a fully commission-based revenue model with Ingram Content Group for its print textbook business. Recall around this time last year, Chegg announced a multiyear deal with Ingram, which agreed to purchase its textbook inventory and allow Chegg to ultimately exit its warehouse business. Chegg anticipates the transition to a fully commission-based model with Ingram to be complete in 2017.

Finally, for the full fiscal year 2016, Chegg anticipates revenue of $230 million to $250 million -- or down 20.4% at the midpoint from 2015 -- pro forma revenue of $170 million to $185 million, Chegg Services revenue of $115 million to $125 million, and adjusted EBITDA of $10 million to $20 million. Here again, Wall Street was looking for much higher 2016 revenue of $281.7 million.

To be fair, investors already expected revenue to decline, and Chegg's more attractive digital model should still leave it a more profitable company over the long run. But considering it not only fell short on overall revenue in Q4 and expects the gravity of that decline to accelerate in the coming year, it's hard to blame investors for taking a step back today.