Amazon.com said Thursday that it agreed to buy education technology company TenMarks, a sign the world’s largest Internet retailer is expanding further into schools.

TenMarks offers personalized online math instruction for K-12 students.

Dave Limp, head of Amazon’s Kindle tablet, e- reader and e-book business, said the company plans to develop educational content and applications with TenMark.

Amazon has made a big push into schools in recent years, entering a market that has been particularly successful for rival Apple and its iPad tablet.

Amazon has been testing Kindles with hundreds of K-12 schools, selling the devices at bulk discounts and helping them purchase and distribute e-books to students. Last year, the company rolled out Whispercast, a service that lets schools manage fleets of Kindle devices from one online location.

Amazon’s education push is part of a broader effort by the company to get Kindles into as many hands as possible. The company often sells the devices at cost and hopes to make money selling e-books and other content such as apps, games, music and video through the devices.

TenMarks has a so-called freemium model where teachers can register and access the company’s service for free and then opt in for paid premium features if they want to, co-founder Rohit Agarwal explained.

“Going forward, we believe Amazon and TenMarks will create significant innovations in the K-12 arena, “he added in a statement.

Terms of the TenMarks acquisition were not disclosed. Subject to various closing conditions, the acquisition is expected to close in the fourth quarter of 2013, Amazon added.