So I tried this idea with Grade 2&3 swimmers, with a small change. Out the end of their middle finger shone a laser beam, with the on/off switch being their belly button. Just in case you were wondering, you need to press it three times to get the red light. Most of the students, after turning it on, could see the laser beam, though some pressed it four times, which meant it went purple!
Next they partnered up in order to watch each others strokes and provide feedback. We do quite a lot of reciprocal teaching in swimming, and this is something they are good at. Person A stood in the shallow end, while person B swam directly towards them, aiming their laser beam at the centre of person A. Person A’s job was count the number of ‘hits’ and ‘misses’ and explain to person B why they were missing, i.e. reaching over the centre line, hands entering the water outside their shoulders or not stretching far enough to get to the centre line.
I was pleasantly surprised how popular this activity was. The students were fully engaged and activity went on for longer than I planned, as there was a great deal of motivation to score as few misses as possible.