So many excellent solutions to a wide variety of questions. If the OP is not a teacher then I suspect he/she is a grandparent or equivalent. I am convinced that what's needed is something robust enough to use out in the field, carryable in a pocket or small pack and non electronic. Small relatives need results fast if you want to keep them interested. I have noticed that the 'quality' factor that adults are concerned with is way down the list for kids. My grandkids play very happily with my old Pentax binos which are well out of collimation; I cannot use the things. Same with using astronomical telescopes. They are looking for different things from adults and the need to be in their teens before they are prepared to deal with the fiddly bits of hi tech equipment.
The microfiche reader would have been great a few years ago (I would have loved one at school) but classrooms tend now to have video projectors and big screens so a USB microscope would be easy to store and hopefully the teacher would be familiar with the idea of using the app - and its filing system.
As always, it's horses for courses. The age of the kid is a major factor.