steve-ss
20 users all log into the same user id and these are the same user home directories exported yes. i think I can see the problem: all users are trying to update ingle .kde files at the same time.
As far as I know, KDE can handle a user which uses his account from different machines simultaneously (it uses file names as .DCOPserver_<hostname>_:0). But there may be a race condition in updating for instance the ~/.Xauthority file. Each kdm session writes an authorization information there and if it fails then X clients cannot access the X server. In other words, KDE cannot start then. I suggest you try a separate account for each machine, e.g. pcA01, pcA02, ...
Is it practical to have 200 different logins on the same server?
You don't need a separate login for each kid, just for each computer. This approach is also used in computer classes on universities. This prevents two users from modifying the same file - you definitely want to avoid this situation. We also have special accounts which are shared by several people but these accounts are used quite rarely.
Will NIS cope with that?
Yes. Anyway, if the disk performance is a problem, then you may try to use a ramdisk or a filesystem mounted by the loop device on the NFS server. -- A.M.