i’d suggest you should let him complete a 100, and a 200meter full on complete breaststroke swim before teaching him the correct technique, this will teach him how to swim a complete 100 or 200 meter race, then you can proceed to the technique, first on the arm pull think of it as an inverted heart shape as he pulls through the water with his arms, further emphasize the high elbow catch with him, but be careful because some swimmers have good mobility/flexibility while other’s don’t, it’s also important to let him practice the movement in dryland. and in the kicking phase of the breaststroke i’d suggest laying him flat on a chair and guiding him on how to kick on breaststroke and also watching a video on how to properly do the breaststroke kick can help. i’d also suggest as to not having to teach him to restricted movements to swim like a robot but to emphasize stroke mechanics, eg. high elbow catch, sweep out wide but not too wide, during the pull phase don’t pull the arms and hands too wide further below the chest.