Oh yeah, the scroll bar students need to use to view all of the source text and questions. The scroll bar can be tricky to navigate on a Chromebook, which is one of the most commonly used devices in classrooms.
A great way to have students practice using a scroll bar, in the context of a classroom lesson, is to use Google Forms results. When you allow students to view each other's submissions, each questions' responses are placed into a small window with a scroll bar. Here is an example from a 4th grade class whose students were asked to come up with things they wanted to know about humans breathing.
Bleow is a portion of the editable version of the form. It only had one question for students to answer, but they were allowed to submit more than one response by leaving the "Show link to submit another response" box checked. They could also view other's responses because I left the "Publish and show a public link to form results" box checked.
Here is what students saw after they submitted their response:
Another challenge students mentioned was the need to view the source text side by side with the questions and figure out how to go back and forth between the two. My suggestion for practicing that skill within a classroom context is to teach students how to split their tabs apart and resize the windows so they are reading an article on the left and typing into a Google Doc on the right. To split your tabs, just click and hold on the tab title and drag it slightly down and to the right. That tab will split away from the others you have open. Then you need to minimize your remaining window and resize as needed. That will take some time to learn, but the kids will pick it up quickly, and learn a valuable study skill as well.
It might end up looking like this:
Guess what? More scroll bar practice with this activity too.
I think that some practice with a typing program is helpful, but you will get more bang for your buck if you can set up activities that are content driven where students can practice these "bubble in the straw" tech moves.