by the increase in excess tax benefit of stock-based compensation.
Comparison of the Years Ended June 30, 2021 and 2020
Revenues. Our revenues for the year ended June 30, 2021 were $1,536.8 million, representing an increase of $496.0 million, or 47.7%, from $1,040.8 million for the year ended June 30, 2020. General Education revenues increased $346.4 million, or 37.1%, year over year. The increase in General Education revenues was primarily due to the 45.4% increase in enrollments, and changes to school mix (distribution of enrollments by school). Career Learning revenues increased $149.6 million, or 139.9%, primarily due to a 126.0% increase in enrollments, school mix, as well as from the acquisitions of Galvanize, MedCerts and Tech Elevator.
Instructional costs and services expenses. Instructional costs and services expenses for the year ended June 30, 2021 were $1,001.9 million, representing an increase of $308.7 million, or 44.5%, from $693.2 million for the year ended June 30, 2020. This increase in expense was primarily associated with the incremental personnel and related benefit costs associated with supporting higher enrollments, as well as costs associated with serving Galvanize’s customers. Instructional costs and services expenses were 65.2% of revenues during the year ended June 30, 2021, a decrease from 66.6% for the year ended June 30, 2020.
Selling, general, and administrative expenses. Selling, general, and administrative expenses for the year ended June 30, 2021 were $424.4 million, representing an increase of $109.3 million, or 34.7%, from $315.1 million for the year ended June 30, 2020. This increase was primarily due to an increase of $39.9 million in personnel and related benefit costs, $26.4 million in professional services expenses, $18.8 million in licensing fees, and $15.7 million in stock-based compensation. The increase in personnel and related benefit costs was partially related to the additional headcount of MedCerts and Tech Elevator, as well as a full year of headcount related to Galvanize. Selling, general, and administrative expenses were 27.6% of revenues during the year ended June 30, 2021, a decrease from 30.3% for the year ended June 30, 2020.
Income tax expense. Income tax expense was $24.5 million for the year ended June 30, 2021, or 25.6% of income before taxes, as compared to $8.5 million, or 25.8% of income before taxes for the year ended June 30, 2020.
Discussion of Seasonality of Financial Condition
Certain accounts in our balance sheet are subject to seasonal fluctuations. As our enrollments and revenues grow, we expect these seasonal trends to be amplified. The bulk of our materials are shipped to students prior to the beginning of the school year, usually in July or August. In order to prepare for the upcoming school year, we generally build up inventories during the fourth quarter of our fiscal year. Therefore, inventories tend to be at the highest levels at the end of our fiscal year. In the first quarter of our fiscal year, inventories tend to decline significantly as materials are shipped to students. In our fourth quarter, inventory purchases and the extent to which we utilize early payment discounts will impact the level of accounts payable.
Accounts receivable balances tend to be at the highest levels in the first quarter of our fiscal year as we begin billing for all enrolled students and our billing arrangements include upfront fees for many of the elements of our offering. These upfront fees result in seasonal fluctuations to our deferred revenue balances. We routinely monitor state legislative activity and regulatory proceedings that might impact the funding received by the schools we serve and to the extent possible, factor potential outcomes into our business planning decisions.
The deferred revenue related to our direct-to-consumer business results from advance payments for twelve month subscriptions to our online school. These advance payments are amortized over the life of the subscription and tend to be highest at the end of the fourth quarter and first quarter, when the majority of subscriptions are sold.
Liquidity and Capital Resources
As of June 30, 2022, we had net working capital, or current assets minus current liabilities, of $648.5 million. Our working capital includes cash and cash equivalents of $389.4 million and accounts receivable of $418.6 million. Our working capital provides a significant source of liquidity for our normal operating needs. Our accounts receivable balance fluctuates throughout the fiscal year based on the timing of customer billings and collections and tends to be highest in our first fiscal quarter as we begin billing for students. In addition, our cash and accounts receivable were significantly in excess of our accounts payable and short-term accrued liabilities at June 30, 2022.