My teachers always told me that there’s no such thing as a free lunch. Apparently, that also applies to Microsoft Office.

On Tuesday, Microsoft announced its Student Advantage benefit, which provides free Office 365 ProPlus licenses to students around the world — if their school buys Office for its faculty.

It’s a nice perk, especially because 35,000 institutions are retroactively eligible for the program when it kicks off Dec. 1. It’s also a clever sales strategy by Microsoft, which is trying to figure out how to sell more Office licenses in an already saturated market.

“We are thrilled to offer Student Advantage to schools across the globe so students have access to the latest, most up-to-date version of the world’s leading set of productivity tools in order to give them a competitive advantage when entering the workforce,” said Anthony Salcito, vice president of worldwide education at Microsoft, in a statement.

Microsoft also provides some free, cloud-based services to schools (like hosted email and Office web apps) with its basic Office 365 Education plan. Two premium tiers, which offer expanded Office 365 functionality, cost a few dollars a month per student (and roughly double for faculty).

More than 110 million students and faculty worldwide currently use Office 365 Education, according to Microsoft, and more than 98 percents of students using productivity software currently use Office.