You can add a minisite to your website that requires a login and is only accessible to people with accounts at your site.
School Loop SLS2
Step By Step Guide
1. Login to your School Loop account and go to Toolbox -> Site Center.
2. Add a Minisite by clicking on Add New - Minisite.
3. Check Require Login box.
Publish Minisite and a login page should come once the user tries to access it. Login credentials should be the same as School Loop's login.