In the past I have worked for a local highschool, designing their school website that allowed their administration to dynamically manage school activities that would be going on at any one time.
I have also created a Project Management system for a web designer to keep track of his clients, associated projects and worklogs.
In addition to these two projects I have also created number client management system for companies.
The proposed system for your project would include the following features,
Front end:
1) Login System, protecting against database injections and brute force attacks.
2) User profiles, assoicated a username and password with student information.
3) Activity search functionality.
4) Activity Description Page showing availability and user registration button.
5) Another feature that I could for see being useful is allowing a waitlist for each activity, so that if a user drops an activity the first member on the waitlist will be automatically added to the activity.
Password Protected Backend:
1)User management system, allowing users to be added, removed or edited manually through the backend of via an uploaded cvs file.
2)Activity management system, allowing for a title, description, maximum student size, possible waitlist size, printable registered user list. As with the user management system activities can be added, removed or edited manually or through an uploaded csv file.
3)Administrator Management System, additional administrators can be added or deleted.