Jorge,
this should be possible (and possibly even simple to accomplish), but first we need to know some stuff:

1. This computer you intend to use as a server, does it have a public IP (meaning, an IP that can be directly connected to from the Internet)? If not you will have to talk to your administrator to set up SSH and FTP forwaring to your server.

2. With Debian, installing the needed software should be easy. The SSH daemon is installed by default so that's no problem. Then you'll need an FTP server so the students can store and retrieve files easily. Or you could set up SSH to allow file transfers but that can be a little tricky for the students to get used to. I recommend ProFTPd. It's easy to set up and works very well.

If you don't need the users to be able to log in and use the computer remotely (except for downloading and uploading their work) you can set their accounts' shell to /bin/false. This will make it impossible for them to log in (from the terminal or using SSH). Then set the variable RequireValidShell in /etc/proftpd.conf for "no" and your students should be able to log in (if you have created accounts for them on the server).

You could also set up NFS shares so the users can copy their files to and from the server even easier. If you have Windows machines in your classroom (or on your network) you could use Samba to create Windows shares on the server as well.


hw