When a site has move than 21 activities or resources enabled on a site the add activity modal requires the user to scroll to find the activity they want to create. Furthermore selecting assignment and then clicking the add button at the botton is a very long mouse movement for the user. The help text also takes up 60% of the modal but is only useful for the first 1 or 2 times a novice teacher has to read about the activity type. This is going to be just a huge pain for intermediate and advanced users who are the majority of your users.

Better usability would have activities in multiple columns see minute 1:50 in http://www.youtube.com/watch?v=5v1njUh1Cj8 for folder views handle of activities or the attached mockup. Help would be moved to a separate modal if the user clicks the help icon or one general help that combined all activity helps.