One thing I would add if the budget allows (i.e. ski school or race club) is getting Coaches Eye. You can use your phone or tablet but the beauty is you can edit on the fly. Things like while playing back the video, you can control the speed back and forth, and you can draw line like you see (or at least used to) the commentators do in football games on TV. This enables you to show the person things like if their shoulders, hips are level, hand placement etc. Just add a line or circle where something should be in contrast to where they are.
I don't know what it costs but there is a free trial period and after that there is a license fee. The club pays for it but I don't think it is a lot, or at least once bought in as a team, additional licenses aren't as much.
https://www.coachseye.com/package/individual
I know I'm not doing that good of a job describing it, but it is well worth it if you are in the business of doing MA. Doesn't matter the sport.
Not to mention that you can now prove to Tommy (soon to be known as Tongueless Tommy) that he did indeed have his tongue out going through the Slalom course:
You even get to play it back to him in slow motion from first poking out to full fledge flapping like a dog riding in a car.