Stacey,
We have used quite a few headsets over the years, and while none of them are perfect, we have been using Califones mostly.
When you say the new computers only have one input for audio/mic, is your concern that two students can't work together on the same computer?, because I believe the audio plug on Dell all in ones is a Universal audio jack that supports both playback (headphones) and mic (for one headset).
https://patents.google.com/patent/US7241179B2/en
In either case, Califone has both analog and USB:
This company also sells Egghead headsets, which are less expensive and have a longer warrantee.
(We have no affiliation with this vendor.)
Bob Majors
Language Learning Center
University of Washington
We are installing new Dell all-in-one computers in my center and I need to purchase new headsets with mics to go with them. I have been holding on to some old Telex Discovery headsets, but I suppose it is time to move to USB – especially since the new computers only have one input for audio/mic. I am looking for something durable and easy to keep clean.