How do kids turn in work?

What's the best way for kids to turn in apps? Must they publish them to the gallery? When they do, can they get a sharable link?

For your own sanity, I would recommend asking for documentation with the apps.
Here's how I document my Power User samples:

Not necessarily, though it has nice facilities for sorting and grouping them it doesn't allow extensions. ((Not that those are always needed.)

Any place they can post .aia exports, blocks images, and documentation works.

Yes, the Gallery provides sharable links. See my doc index.

Given they are likely to all have google accounts (?)....

Set up a shared folder for each student to upload their work on Google Drive

This is a issue you need to decide Kim.

What is more important to you: the compiled app, how the app was constructed (the aia) . What you do depends on the criteria you agreed with the students for coding and how well they do it. Isn't that true.

Students could build the app at the end of the Project (Build > Android App) to produce the QR code like this.

Copy the image using Snip & Sketch

Send the image to you using email. The QR code is sharable for two hours.

Instructor loads the app on their device using the image (if you do it within two hours of the student creating the apk.). Yes, you can use the student made image of the QR code to link to the server and retrieve the apk.