I would say that if this is going to be the student's primary computing device: First, have them check the requirements for their program and specific classes to make sure an iPad will meet all the requirements. Second, get either the 13" Air or Pro.
If the iPad is for notes in class and work on the go and they'll have another Laptop or desktop computer, an 11" could be a viable option. Honestly, I can't say anyone can notice much difference between the M2, M3 or M4 in 95% of the apps and tasks you'd run on an iPad. Video Editing with Final Cut or Davinci Resolve is probably where you'd see the differences. I'd prioritize storage over the latest chip. In most cases I'd rather have an M2 iPad Air with 256GB of storage than an M3 with only 128GB.