Is there a different way I can code Android apps? Like in a browser, I am using Chrome OS.

Well, this is a school computer. So, would I have to pay for a flash?

For a flash drive to like, boot off usb? Not for this method, crouton is downloaded and then run through Google Chrome's terminal. Or if your talking about like, flashing the BIOS or running some particular start-up or restore method beyond enabling/disabling the developer mode, that shouldn't be necessary either.

Hmm. It being a school computer changes some things as far as my recommendation though.

If it's a situation where the school is like, "Hey we're letting you use this, but you better not be installing anything outside of ChromeOS on it!" (if it's part of your school's computer lab or library or whatever), there is a chromestore app called Caret (https://chrome.google.com/webstore/detail/caret/fljalecfjciodhpcledpamjachpmelml?hl=en) that I'd reccomend.

It's a basic, but pretty nice and functional, text editor. Using Caret in ChromeOS, you could write your Android code in Java and then move onward from there. Obviously, you'd be lacking some of the helpful features of Android's dedicated IDEs, but you could follow along with a good amount of Treehouse's stuff and then export or copy paste those xml and java files into a Computer that has eclipse or Android Studio at a later point, and then there's your emulator testing and your debug options, etc.

If it's a situation where the school maybe loaned you a laptop and wants to make sure you're not doing anything that's going to break their computer, but still gives you some freedom to mess around with it (for example, if you just have to turn it in the way you received it at the end of the year or restore it to how it was at the end of the week or something), the ChromeOS/crouton method is actually pretty helpful in this regard. The computer under crouton boots up in developer mode. Turning off developer mode actually wipes the hard-drive of everything you installed on it and restores the computer back to a fresh ChromeOS. If there's a specific suite of programs the school runs on the machine you might have to reinstall some stuff through the Chrome webstore but as a rule, chromebooks are really hard to brick and really easy to restore back to 'clean' installs.

Not knowing the particulars of your situation, I'd say try Caret in ChromeOS for now, so you can at least be able to write out some android code with nice syntax highlighting and familiarize yourself with the language, and then talk to some folks in charge at your school and figure out what they will and won't let you do with the device for anything like installing crouton and another OS beyond that. Hope this helps!