The recommended minimum bandwidth is 1Mbit. 1 minute of recorded audio (usually mono) takes 1 megabyte to save and 1 megabyte to load, which then means about 10 seconds of waiting time. For simpler projects this should be enough. However, if you do longer projects, for example 30 minute podcasts or project containing a lot of dense audio tracks, you might want 3-10 Mbit to experience faster saving and loading.
In a classroom setting, there will probably be a lot of loading happening simultaneously, especially when students are instructed (e.g. browsing loops). Saving, on the other hand, will probably be spread out more evenly over time as students make progress. A rough recommendation is 20 Mbit per active classroom.