I thought this was an outstanding piece of TV let down by a lack of script editing.
Others have picked up on the school, for me it was that a tradesman not knowing what he needed to remove an oil based paint, going to a DIY store instead of a builders merchant, and then not having membership or taking a receipt.
It is inspired by true events but is not a true story. The writer admits it's pretty much just his musings as to why recent murders of teenage girls by teenage boys have happened. This is not a reason to not make something, far from it. Why is far more interesting then following a reenactment of real events, and acceptable to explore when not a real case and victim. However, it makes wrapping the why and unknowns around in the real and true even more important to not lose the viewer.
The why given by the writer is toxic masculinity which is woven throughout the show from the very first scene of the over wise good sort but not very good and we don't know why father and DI farting in his female colleagues car. Some are obvious, too obvious, like the late and raging male teachers. Some more subtle like the female school worker forgetting to introduce the female DI, and then correcting herself.
This explodes after the tedious car journey which is far too long but lays the ground for what comes next and after that, but still could have been shorter. The most important scene in the whole show for me is the parents coming to the realisation that they were of some fault and maybe even what that fault was, and a fault which I think many parents and I include myself can relate to and may even be guilty of or could be.
However for me this was let down by one line "I was looking up gym stuff and suddenly I get all this anti woman stuff" which jumped out to me as too obvious an attempt to remove any ambiguity, and the writers rather then the characters words. I later saw this line word for word from the writer across multiple articles
One thing thrown in here is the Mum saying I got home sooner, in one throwaway comment it is revealed that they both work full time even though the Dad has his own business employing other men and puts in 14 hour days and Mum "a fine woman" with an immaculate home seemingly playing the traditional homemaker.
The twist of dripping in hints that Jamie may have been bullied by the victim and there could possibly be a palatable explanation and then in the phycologist scene finding out he wasn't and there isn't for me adds layers and richness, and is the "who done it" moment.
The one take was a great technique for this piece and had reason to ground the viewer in reality, but was overall sadly let down by a lack of reality in places which I'm surprised was allowed to pass in such a high budget, time consuming and overwise carefully crafted piece.
But overall bravo!