To see what settings _actually_ are, you can issue (if you have command line mysql access) the following command:
show variables;
Or perhaps if you have phpMyAdmin access, click on 'Show MySQL system variables'.
If the value is zero, then you're not applying any limit.
Regarding Marcio's question, this value (max_user_connections) isn't directly translatable into figures about the maximum number of concurrent users.
This forum is a great place to get advice about your setup. Try posting some details on how many students you'll have (and their usage patterns) and what type of environment you're using to host Moodle (hardware and software specifications)... and see if we can help you out.
MC