How to best use lab periods One of the major uses of my classroom time is for lab work. This is both a requirement of the AP Computer Science curriculum, and also nominally a benefit, as it allows me to walk around and answer questions.

In practice, however, I have found that the students work on their tasks, and whether they are doing well or not, they don't ask questions, even when prompted individually with a "how's it going? Do you need any help?"

This eventually results in me going to sit down at my own station to do other work for about 10 minutes, and then making the rounds again.

This feels like an underutilization of myself as a resource. It's not as if I don't have students who struggle, and there are always students who fall behind and submit their labs late.

So, how can I better utilize the lab time? Are there techniques to get kids to ask questions when progress slows? Or is there something else that I should be doing altogether?
The problem you describe doesn't exactly fit this answer, but it might be useful to some with a similar problem. 

In some such labs it has been observed (and filmed) that students working alone at a station get into some difficulty and raise their hand for help. If the instructor and/or assistant is busy with another at the time, the student with the new problem waits. Then maybe another, and two are waiting, etc. 

The solution to this is to have students always working in pairs in the lab, doing things like pair programming, pair research, pair writing (very creative), etc. This has been observed to reduce the waiting to essentially zero as the students solve their own problems. When one student gets "stuck" it is unlikely that the partner is stuck in exactly the same way so they can move on. This is a well known effect in professional pair programming also. 

You still need to wander about asking if you are needed, as a pair will sometimes queue a question till you come around while they work elsewhere. 

Sorry, I don't have a link to the study on this. I assume it came out of the Agile Community's educator forum.