What’s the difference between the iPad and the iPad Air?

All current iPad models all run the same full iPadOS.

All current iPad models all either use the original, 1st or newer 2nd gen Apple Pencil.

( iPad 8th gen and iPad Mini 5 all use the original, 1st gen Apple Pencil )

( 2018 and 2020 iPad Pro and 2020 iPad Air 4 models use the 2nd gen Apple Pencil )

So, iPads are more like cars, now.

You are paying for iPad optional features, now.

Do you want/need larger internal data storage space for data, like music. movies and photos/images and room for other types of data?

Do you need a larger or smaller iPad screen?

Do you need/want an iPad model in a variety of colors?

Do you want/need a bonded, laminated display?

Do you/want/need higher color gamut display with Tru-tone room brightness calibration?

Do you want/need faster, more powerful internal CPU?

Do you want/need more internal processing RAM?

Do you want/need better iPad cameras?

Do you want/need better/more iPad speakers?

Do you want/need the improved, 2nd gen Apple Pencil?

Do you want/need to have the new Magic Keyboard portfolio for the 2018/2020 iPad Pro/iPad Air 4 models?

All of these options are what you need to decide if you really need, or not, and to decide to pay for accordingly.

The more iPad features you decide you need, the more you pay.

It all comes down to how much money you are willing to spend on iPads with additional, premium features.

You can now pretty much do everything on any current iPad model, now.

All current iPad models are sufficiently powerful enough, today, to do pretty much any task put to them now.

https://www.apple.com/ipad/compare/

Purchase the largest internal data storage capacity iPad model you can afford as no Apple mobile iOS/iPadOS devices have ANY internal expandable storage.

The “iPad” is the entry-level (and cheapest) model of iPad. At the other end of the scale you will find the flagship of specification and performance in the iPad Pro - with prices to match. The iPad Air4 sits between these two extremes, providing high performance without some of the more advanced features and hardware.

Apple offer a useful page where you can directly and usefully compare major features of the various iPad models.

If the iPad is intended to be used in an educational environment, in may be worthwhile to seek advice from the educators - as they may have specific recommendations in context of appropriate devices for the classes in which the device might be used.

iPad - Compare Models - Apple

Apple provides a good comparison page for you:

https://www.apple.com/ipad/compare/