There are other teachers on here who have hatched in the classroom. Hopefully they will chime in if they see this post. I'd suggest you may want to start a new thread with a title something like "hatching in the classroom" to get their attention.
I haven't done it so hopefully any misinformation I give you will be corrected by those with experience. But my opinion is:
Make sure your incubator has an automatic turner. You can get some to hatch if you don't turn them in the evening and on weekends but your hatch rate should improve if you can follow the book.
You need to turn the automatic turner off after 18 days, so I would set them so day 18 is a school day. I'm torn between Monday and Friday as the best. If it is a Friday, the incubator will not be opened and humidity upset since no one will be there. Some chicks may start a little early, but your kids should get to see the pipping and zipping from most of them on Monday and Tuesday. The chicks can last for two or three days after hatch without food or water and the hatch should be over by Tuesday or Wednesday, so you can take them out during the school week. If day 18 is Monday, you will be there to adjust the humidity during the last few days when it is most important. Your kids will see the pipping and zipping, but the hatch may not be over with by Friday, so you would not be there to take the chicks out to feed and water them when they need it. You could have a hard decision on Friday if the hatch is not quite over. I'm not sure which I would choose. I'd probably change my mind a few times, but I think I would set them Tuesday morning and turn the automatic turner off end of business Friday. That way they should see most of the hatching process Monday, Tuesday, and Wesdnesday and you can take the chicks out when they need it.
Are you in touch with your county extension agent's office? They should be able to give you good information and access to equipment, supplies, and hatching eggs. And they should be able to find you some experts to talk to your classes about the process.