Q: How to hide materials in iTunes U Materials Library

When creating an iTunes U course for the high school level, my teachers would like to hide online quizzes and some other documents until students reach that topic.  Is there any way to hide items in the Materials Library from student view until they are needed in the course?  If no, is there a way to completely hide the course materials so that students have no access to it?

This is a huge problem that I know other districts are struggling with.

Thank you,

haygoodjb