Web Dav File Share Issue: Read/Write not correct

I am using Mac OS X Server. I have created groups and set up folders in file sharing. I have created certain folders as read only for group members and other folders as write only. This way, when students use, they can open documents from read folders and submit work to write folders. However, when logged in, students can see all folders. In other words they can read a folder that is write only and they can write to a folder that is read only.

Any suggestion or help would be appreciated.