Net income for the full year was $147.7 million or $2.18 per diluted share compared to $95.9 million or $1.39 per diluted share. Adjusted earnings per diluted share, which, again, we believe is more indicative of our underlying operating performance was $2.10 as compared to $1.63, reflecting an increase of 28.8%. For the fourth quarter, adjusted operating income was $19.4 million as compared to $32.4 million in the prior year quarter and adjusted earnings per diluted share was $0.27 as compared to $0.31. While this anticipated decrease was primarily due to lower revenue at our academic institutions, it was actually better than what we had expected. For the fourth quarter, revenue at CTU was lower due to the academic calendar redesign and the resulting lower revenue days, while revenue at AIU System was lower due to the peak impact of the operational changes made earlier in 2023 that was experienced in the fourth quarter results.
Full year revenue increased to $710 million as compared to $695.2 million, while revenue in the fourth quarter decreased by 16% to $147.9 million. Both institutions experienced sequential improvements in student retention and engagement throughout the year. The full year revenue comparability was also positively impacted by the academic calendar redesign CTU as well as the acquisitions completed in 2022 that were not part of the full comparative prior year period. As it relates to total student enrollments, total student enrollments for CTU increased by 3.2% as of December 31st. And as expected, AIU System ended the year approximately 39.3% lower. Despite a negative impact from the academic calendar as it relates to enrollment base, growth in total enrollments at CTU was supported by organic improvements in student retention and engagement.
As it relates to the AIU System, lower total enrollments were in line with our expectations as discussed during prior quarter’s earnings call. This decrease was driven by the short-term operational changes and adjustments within prospective student enrollment, marketing, and outreach processes undertaken earlier in the year to ensure compliance with anticipated and final regulatory changes. While these operating changes and adjustments were necessary, we are pleased to share that as planned, marketing and student enrollment activities have mostly reverted to normalized levels and we expect AIU System to experience double-digit total enrollment growth in subsequent quarters during 2024 as compared to the fourth quarter of 2023. Now, to our segment results.
Full year revenue at CTU increased by 11.8% to $468.9 million due to a positive timing impact from the academic calendar redesign and the 2022 acquisition as well as underlying organic growth in student enrollments. As expected, fourth quarter revenue at CTU was 3.6% lower than the prior year quarter due to a negative impact of the academic calendar on revenue earning days during the quarter. Operating income was $25.4 million for the quarter as compared to $34.1 million in the prior year quarter, while full year operating income increased by 1.7% to $144 million. Please note that the operating income for the quarter was impacted by certain nonrecurring charges related to recent acquisitions. At AIU System, full year revenue decreased by 12.5% to $240.3 million, while fourth quarter revenue was $43.2 million or 36% lower than prior year quarter.
Please note that the peak impact from the operational changes undertaken within AIU System was experienced in the fourth quarter of 2023. Operating income for the quarter was $0.6 million, while full year operating income increased by 35.9% to $45.3 million. Despite the revenue decrease, full year operating income increased primarily due to lower marketing and admissions expenses. AIU System will see some of this operating leverage reverse in 2024 as it reinvests in its marketing and admission functions. Overall, we ended the year on a high note as it relates to student retention and engagement and as we enter 2024, we expect to operate at levels consistent with the second half of 2023. Moving on to corporate and other. Operating losses for the quarter and the year were $10 million and $38.8 million, which improved 32.6% and 14.2%, respectively, as compared to the prior year period.
This improvement was driven by a decrease in legal fees primarily associated with the responses to the Department of Education relating to loan forgiveness applications by former students. Please refer to the disclosures regarding Board defense to repayment in our 10-K that was filed this afternoon for additional information on this matter. Now, turning to income taxes. For the fourth quarter, we recorded provision for income taxes of $5.2 million. This resulted in an effective tax rate of 23.2% for the quarter, bringing our annual tax rate to 23.1%. The effective tax rate for the quarter was positively impacted by approximately 3.7% as a result of the release of previously recorded tax results for uncertain tax positions. The full year tax rate was positively impacted by the tax benefits associated, which are previously disclosed prior year ordinary loss attributable to the stock of a subsidiary, which decreased the effective tax rate by 2.4%.
Finally, we expect that for full year 2024, our effective tax rate will be between 25.5% and 26.5%. Now, to our balance sheet and liquidity. For the full year 2023, cash flow from operations was $112 million versus $148.2 million in the prior year. We ended the year with $604.2 million of cash, cash equivalents, restricted cash, and available for sale short-term investments. This represents an increase of approximately $86 million over the year-end 2022. Some of the key offsets to the positive cash flows from our academic institutions were $41.8 million of income tax payments, $22.7 million in return of capital to shareholders, and $6.4 million of capital expenditures. Finally, we expect that our 2024 ending cash balance will continue to grow as compared to year-end 2023.
Capital expenditures for the full year were approximately $6.4 million or 0.9% of revenue. For full year 2024, we foresee capital expenditures to be approximately 1% to 2% of revenues. Before I share the updated outlook, let me take a minute to discuss capital allocation. We were pleased to announce that consistent with our dividend policy, on February 5th, the Board of Directors approved the fourth quarter 2023 dividend payment of $0.11 per share payable on March 15th, 2024, to the holders of record of Perdoceo’s common stock at the close of business on March 1st, 2024. To provide context, on an annualized basis, this quarterly dividend represents roughly 27% of our trailing 12-month free cash flows. Future quarterly dividend payments are expected to be paid out of the free cash flow for the relevant year, subject to Board approval and the company’s available retained earnings, financial condition, and other relevant factors.
