Redirect Using Rules Based on Account Role
Check that you are not using any other contrib modules like Login Toboggan which may be setting a redirect after log in.

Failing that, turn on Rules Debugging by going to admin/config/workflow/rules/settings and ticking the 'Log debug information to the system log' checkbox.

Log out and log back into your site as a student user. Then go to admin/reports/dblog and check the debugging messages set by Rules. 

You will then be able to see which of your conditions is failing.