Setting Student Upload Limits
You can limit students' uploads either by the number of submissions OR by the total Prompt spend for the student. Note that limiting a student by number of submissions counts all student submissions (whether they were sent to Prompt for review or not). Submissions that are uploaded without a request for feedback, and submissions that are returned to the student without feedback are counted against a student's upload limit. The Prompt Spend limit counts only the total spend of reviews sent to Prompt for feedback.
The limit can be set on the students tab of the Organization page. Click the Manage button for a student, and in the popup that appears you can adjust the upload and spend limit for the student: