file permissions and security

[Estefania]

Hi all, I`m the network administrator of a computer lab in a school.
My server (Win 2k) has the following shares
\\server\asignature\PRACTICES\user
and also
\\server\asignature\LESSONS\user

Each user has the right to modify everyting on their own folder (no matter
if it is the folder in PRACTICES or LESSONS)

When the teacher is going to take a lesson, I give them access to the folder
LESSONS, otherwise it is blocked.. How do I block the folder?... I created a
group called "students" and for that group I deny any permissions.

But I figure out that if them go to Start>Run> and type
\\server\asignature\LESSONS\user
they have ALL the rights to change their files, no matter that LESSONS is
blocked for their group.

Why there is no blocking for the students in the folder LESSONS?
Is obviously they are the owner of their own folder, but they should not be
able read anything on it
Any idea? Thanks a lot