Social learning company Grockit has closed its $7 million Series D funding round. The round was led by Atlas Venture, a previous investor in the company. Returning investors Benchmark Capital and Integral Capital Partners took part in the round as did new investors NewSchools Venture Fund and GSV Capital. This brings Grockit’s total funding to $24 million.

Grockit helps students prepare for tests by letting you study with your friends and learn from its instructors. You can track your progress using quizzes and practice sessions and test yourself with full-length CATs. The service brings together social networking and online game technology to provide a fun way of learning academic skills and achieving better scores on standardized tests.

More than 1 million people have used Grockit to prepare for tests successfully. Compared to those who choose to study independently, Grockit claims that students who use the service spend 30 percent more time answering questions, solve more than twice as many problems and are around 10 percent more likely to answer questions correctly.

The funding will be used to help Grockit grow domestically and internationally, but it is already growing substantially. The company is teaming up with higher education institutions to provide test preparation facilities to students. Georgetown University in Washington will this month start offering students and alumni access to Grockit’s GRE, GMAT and LSAT test prep programs. Similar programs will be rolled out at other universities — both in the U.S. and internationally — in the coming months.

“We’re growing quickly, and now is the time to accelerate the business. Every day, we add the equivalent of one American high school to our user base,” said Roy Gilbert, Grockit CEO. “While we continue to build from that momentum in the next year, our goals and focus will remain the same: to help more students learn by using the incredible power and scale of the Web.”

Over the last month, Grockit has hit a significant milestone — 10 million questions answered by students — while it added integration with Facebook‘s Open Graph API (which was updated last month to make social sharing easier and more passive) to make learning and studying more social. The company introduced a new business model, where it will provide one year of free access to Grockit Academy to an under-resourced student for every account that is purchased, and it has expanded in India to help students there study for the IIM-CAT, a required test that’s part of the application process for one of India’s main management schools.