I actually agree with SpiiderMan83 on this re Brad and Terese's doubts.
We, the viewer, saw the altercation so know that Elly was in the wrong, and indeed that she has been provoking Piper for weeks.
But, the trouble is Piper was instantly antagonistic towards Elly because of her flirting with Tyler and did make uNjustified (at that stage) accusations on her vlog and, if you recall, called her a skank in front of everybody when forced to apologize.
So, I can understand why they might consider that this complaint against Elly is just another way for Piper to get at a woman she has made it clear she doesn't like and resents being in a position of authority.
Brad also has the additional complication of having to be seen to be impartial and not giving his children special consideration at School. In this situation, he is not just a parent, but a member of the teaching staff so is required to show loyalty to them and generally, the assumption would be made that it is the teacher, the adult who has had training will be the one telling the truth rather than the child, especially a child that has a proven history of attacking the particular teacher, both physically (throwing the drink at her), verbally (insulting her when forced to apologize and in class) and online (her vlog the day after the dance).
Brad is in an impossible position really - such issues are the reasons my Mother turned down a job she was offered at the School i was due to start at the following year - she was insistent that she would never teach at a School either myself or my brother were a pupil at as it makes it so difficult for both the Teacher/Parent re conflict of interests, or suspicion of that and the child re bullying or again, being accused of getting preferential treatment.
So, Terese should be the parent dealing with it, fighting her daughters corner but again, i can see why she has doubts (Piper is rather like Matilda in this) plus Elly has found her weak spot with the cameras and losing Lassiters.
I also agree with another poster about the marking. If that project is on the syllabus, there will be instructions as to the marking criteria, specifically whether it is on the individuals contribution or the end, or the end result as a collaborative project. Just check that and also whether there was a difference in the marks between students in other groups.
I'm not defending Elly by the way, I think it is quite clear that I think she's a horrible person and a Teacher should never behave as she does, no matter how provoked.
But, i can understand why Brad and Terese, and everybody else, haven't immediately taken Piper's side over it.