Well, there's two ways you could operate an ISA:
1. You invest $20k in each student, carefully selecting only the applicants who are most likely to succeed, and giving them the most impactful, high-ROI courses you can, so that they almost all repay at least $20k
2. You invest $500 in each student using prerecorded video classes and assignments graded by unpaid 'mentors', take on far more students, and every time you luck into a student who repays $30k that's pure profit, baby.