Hi Dilvan,
Geb is test framework agnostic and has no concept of feature/test. It is in general a browser automation solution written in Groovy on top of WebDriver and it comes with a number of integrations for test frameworks - Spock, JUnit and TestNG. So if you already have anything built for automatic assignment grading using any of the frameworks mentioned it should be trivial to adapt it to be used with Geb.
I hope this helps but don't hesitate to ask additional questions if you have any.
Cheers,
Marcin