Teaching physical education, I’ve never had my own student teacher, but I’ve helped quite a few who were working under colleagues to give them a different perspective. The most common thing I’ve heard from them is “the kids aren’t doing what I told them.” Pretty much every time my reply was “They’re doing EXACTLY what you told them. The problem is you weren’t specific enough, so they’re filling in the blanks.” I always got that “you’re absolutely right” look. The younger they are, the more specific you have to be. I currently teach pre-k 3 and 4, and a kindergarten PE class. Talk about having to be specific

Although, I entertain myself and whichever TA is in the gym with their class by occasionally not being specific just to see where it goes and to have a good laugh. Works every time.
One time a new TA was all frustrated because the kids weren’t getting the concept of the game we were playing. She tries to correct them and you could just see the anger in her eyes from hearing me say the same thing at least 100 times. I go over to her and say “of course it’s a disaster. They’re 3. They’re not going to get the concept in 20 minutes. Let them have fun with it. They’ll get it eventually. It’s called organized chaos.” 5 minutes later she’s still got the look and still can’t handle the kids not doing what she thinks they should be doing, so I say “They’re not going to get it for a few classes. Now get off my floor so I can teach.” She’s sat in the corner and only gotten up to take kids to the bathroom since then, going on 4 years now, so it worked out for everyone.