Just give it to them as a free account, I expect the account would be tied to the professors email address for a record. I would print up some cool stickers of

Just give it to them as a free account, I expect the account would be tied to the professors email address for a record. I would print up some cool stickers of your logo and send them to the professor to handout to the students using your API. Maybe give them a tutorial on ways to limit/cache API requests so they don't overload your servers. Good will like this could go a long way leading them to recommending you when ever they can in the future. Everyone loves stickers they will end up on their laptops and computers and will be a reminder to use your service in the future.