Hi Sue,
As Dan points out, the fact that CODAP becomes fully resident on each user’s computer should rule out any problems with large numbers of users.
As to stability over time, CODAP is evolving so there will continue to be improvements in performance and usability as well as enhanced features. It’s certainly possible that some changes in CODAP will require changes to the instructions in the course materials. One way to deal with this is for your institution to serve a single, stable version of CODAP during a run of the course. This is very straightforward, amounting to little more than unzipping a file onto your server and pointing your users to that URL.
Hope this helps,
Bill