Reply: Thanks for your question, Tim. The PZM-10 is suited for security/surveillance recording rather than for natural-sounding speech pickup. Also, the PZM-10 is designed to be flush-mounted in a surface. Its sound is degraded if it is not flush mounted. A better choice might be the PZM-185, which lies flat on the table and sounds more natural (hi-fi) than the PZM-10.
However, the PZM-185 has an omni-directional pickup pattern. It is sensitive to sound from all around the microphone, so it might pick up too much background noise and too much of the teacher.
How about a Crown PCC-130 instead? This small mic lies flat on the table, and has a uni-directional (cardioid) pickup pattern. It rejects sound coming from behind the microphone, such as the teacher and students at other tables. You'd place one PCC-130 near the edge of the table farthest from the students. If the table is very wide, use two mics about 4 feet (1.2 m) apart.
Another option for miking the students' tables, perhaps the best option, is the Crown MB-4. It's a very small surface-mounted cardioid microphone. It costs very little and rejects sounds behind the microphone.
Listed below are approximate street prices in USD for the Crown mics mentioned here:
Ideally, you would feed all the mics into an automatic (gated) mixer such as the Shure SCM810 (www.shure.com). This type of mixer turns on only the mic in use, which greatly increases clarity and reduces background noise