I think systematically tracing code, line by line, is an integral part of learning how it works. I've modified one Event from a Pong program, written with App Inventor, so that it works badly and students are asked to write down how to improve it. I've included comments on the code so as to model commenting code as another good practice. I'd anticipate this to be one of a series of worksheets. This one I would categorise as "easy" but still anticipate that some students will find it challenging.
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