We've had many teachers and classroom hatchers on here. How many eggs are you thinking about incubating at one time and what is your $ range for an incubator?
Temps need to be fairly steady and it depends on which kind of bator you use as to actual temp settings. A still air needs to be 101-102F near the top of eggs. A forced air needs to be 99.5. Humidity is an issue that will get you 101 opinions, but in actuality it is just a matter of what works for you and your eggs. There are too many variables to say "x" humidity is the ideal. It's not hard to keep track of whether your humidity is optimal and when or if to adjust. Monitoring the air cells (what I choose) or weighing the eggs will point you in the right direction. You can read more about that here:
http://letsraisechickens.weebly.com...anuals-understanding-and-controlling-humidity
Are you looking at getting local eggs or shipped eggs. Shipped eggs in general have a much lower hatch rate and can be a pain in the butt with misshapen air cells and damage. Are you looking for a specific breed or will any do? The big thing of course is having a place fr them once they are hatched.
Will you have an automatic turner (best idea for classroom) or hand turn? Chicken eggs take 21 days to hatch so plan ahead for a day that is a school day so the kids don't miss out.
There's lots of us here willing to help you along from beginning to end. Just note that we all have our opinions and many different hatching philosophies. That's the one thing that you can count on....lol Many different opinions and various experiences. You can almost always find lots of help here:
https://www.backyardchickens.com/t/978237/she-said-he-said-whos-right-whos-wrong-no-one
We have a variety of opinions and you can find help with just about any incubator, because collectively I think someone has used just about all of them at some point....lol