I've noticed that sign up page was http only and felt quite uncomfortable.
A couple of problems:
1. Student data is highly confidential. All traffic should run over HTTPS if you are transmitting student names, grades, etc.
2. Passwords must be encrypted, not sent via a simple POST
3. How do you plan on competing with the large gradebook providers? A lot of districts require their schools/teachers to use a centralized system or at least a common gradebook-type system.
An Error Was Encountered
Error Number: 1062
Duplicate entry 'yaraci64' for key 2
INSERT INTO `gm_courses` (`user_id`, `name`, `email`, `public_code`, `is_public`, `created_on`) VALUES ('3333', 'A', 'yaraci64', 850393, 1, '2010-02-04 16:37:46')
I could not reproduce the issue again, though.