Chromebooks have screen capture tools directly built in to them. This how-to guide is everything one need know about it, but to summarize it, follow these steps:

1.  Click into the quick settings in the bottom right corner (click the clock) and select the "Screen Capture" 

2. A menu bar will appear, and with it you can toggle between the camera (screenshots) or the recorder (video) icons and select the portions of the screen you'd like to record.

 3. Specifically to the Recorder - within the cogwheel you can turn on or off Webcam & microphone, alongside a few other settings. It's pretty intuitive and when done, students just need hit the red recording button to stop their recording. 

4. When you're finished recording, click on the "Stop" buttonto end the recording. The video will be saved to your Downloads folder by default.

Screencastify can be used an alternative to accomplish the same task - and comes with its own suite of additional perks. 

Google Help Article: https://support.google.com/chromebook/answer/10474268?hl=en

Video Tutorial: https://youtu.be/s2bTw_ypw5M?si=WyI1TqHrcFZJqZgT