There are a lot of online coding resources popping up all the time. With websites like repl.it , gitpod.io, and codeanywhere.com you can code with only a browser.
However, you have mentioned college level courses. Most college level coding is going to need a keyboard. Will your iPads have keyboards? Possibly a mouse too.
Most serious coding is also going to need a larger monitor. Would a laptop give students a larger screen? If you are looking at cheap laptops then maybe not.
Again a trade-off. Many of the online coding tools do charge a fee. Running open source software on a laptop could be cheaper long term.
Many schools are going with Chromebooks. Chrome OS will run Linux development tools if it is enabled and the Chromebook has enough power. Enabling Linux on school Chromebooks is often seen as a security issue.