how to set permissions recursively

[skopel]

My users can ftp html documents into a directory called public_html in their home directory. I want the teacher to have write access to these files also..so I added the teacher to the users group and I would like the ftp'ed files to have default permissions 664 so that the teachers can write them. But invariably the defaults are 644. I set umask 002 for the public_html directory and it works for files created via touch but not for files ftp'ed in. How can I get the teacher to have write access to these files? It doesn't have to be via group permissions: that was just an idea.
muchas gracias...

[wmHardRock]

chmod -R 644 blah

[skopel]

I guess I didn't make it clear...when the files are ftp'ed they have default permissions of 644...I need the default to be 664...
I don't want the user to have to telnet in and execute a chmod each time he ftp's a file..I want the 664 to happen automatically
sorry