I find that things can get a bit strange and startling here also.
Dd is 5 and started a mainstream school this September after being in a very small Montessori since she was 3yo.
Now we have a trampoline set up for her when she comes in from school, and she will bounce and let off steam physically, and vocally for 10 minutes or so when she comes in, and is so much the better for it.
We also try and get her to the local playground for a run around before she comes home, and give her a snack there, if weather permits.
I've also found that with limited toilet facilities, the teachers don't encourage drinking water during class, and tantrums can be the result of dehydration, so i always get DD to drink a large glass of water before we go off to school, and I have a large bottle of water for her in her school lunch box that she can sip during her breaks, and I also bring a large bottle of water to the park as well.
We talk a lot about feelings like frustration, anger, fear (and also co-operation team work and kindness) at dinnertime so that she can label what she's feeling and know that it's just a feeling, and needn't be anything more than that. We make funny faces of the feelings.
I find that when she's in a twist after school, and none of the above work, something has actually happened, like falling in the yard, or feeling unsupported about something (sharpening pencils or some other major event ) and with a little investigation, I usually find out what's eating her. Then we all talk about similar experiences at dinner time with a resolved outcome. We draw what happened and make stories out of events also.
Also, I try and remember that DD is being exposed to other peoples' bugs and her immune system is being challenged, so she might not feel 100% all the time, as her system is developing resistance.
All these factors contribute to a change in DD. She's doing the best she can, and I also am looking forward to 'having her back' over the hols.