In fairness, and to think a little more about your throw-away joke than I suspect you intended, the 'push and forget' nature of a button as compared to holding

In fairness, and to think a little more about your throw-away joke than I suspect you intended, the 'push and forget' nature of a button as compared to holding up your hand is important in some situations. The Software Carpentary workshops that I've worked with/seen, for example, use a post-it note system that signifies that a student has a question (or is done, depending on the colour of the note). This allows the student to continue trying solutions without holding up their hand looking for attention. When an instructor is available, they can go over and help. The advantage of a button system, then, would be that you could gather data on which students were asking the most questions, how long they generally have to wait, etc.