So, at my kids school (we are Scotland), you don't need a formal diagnosis. So we had measures in place before we even submitted for one - as they wanted to see if they helped first. If they measures that SEN kids need works then it is basically like a confirmation investigation is needed - if that makes sense? Eldest has ADD (with Autistic traits). Youngest we are awaiting a rediagnosis on as the SEN teacher (who is also parent to an autisic boy!) is like 100% he is autistic he is a carbon copy of my son - doc said naur...Sen teacher is like WTF!
They get out early for classes and lunch - even for the bus if that is an issue. They get to sit in the quieter areas of class. and Just in general all the teachers are - within reason - mindful of their teaching approach. I so think the quiet SEN kids are so much easier for them than the Hyper ones though. And that also played a part in my daughters resistance to going to school. She has about 3 disruptive kids in her classes in s1-2 that basically made her hate school so much that there were tears, stomach aches, headaches, purposefully hurting themselves to get collected (attendance was like 87%). We/school didn't start looking at her as SEN until mid S2 after she decked someone when she was confronted and couldn't flee (and other things)
Currently we are still often 3-5 mins late. BUT our school does reg, so they are never late for actual classes.
My Son also hides in a quiet zone if he is on time/early, and will be the last to go in. He has normal headphones (though noise cancelling ones). Eldest has in ear ones she wears in class with the keep aware on.
NONE of the measures needed have any impact on anyone else.
The school is locked/secure exit, so if they get out 5 mins early for a class, they cant leave the building as a whole.
Only place to skip class is library - and any non senior level kids will get asked why they are there in class time if they shouldn't be.
There are other smaller things that they implemented, and it actually HELPED my eldest with her executive functioning. Yes, morning still SUCK, but she has gone from a chaotic hamster to understanding her schedule in about 2-3 years.
I think the rule of missing class when your late it actually ridiculous, and could it possibly be against her rights to schooling?
As a punishment it teaches her nothing. It is NOT how the majority of the real world functions (yes, buses,trains,planes etc).
I would guess that the missing of so much work will be adding to stress for her, which will make her not want to go to school more, so there will be less and less desire to even bother trying to get there....and that will just keep repeating that cycle.