My experience. DD also not very bright.
We sent her to an outstanding state academy. It ticked all of boxes and seemed a fantastic school from the outside.
People do all sorts to try and get their kids into this school as it very oversubscribed. My DD was able to gain a place down to being adopted from local authority care. We were really pleased to get her in.
The first year was ok - not amazing but OK. They initially provided some additional academic support for which we were grateful but she wasn't fully settled and we put it down to the pandemic disrupting the school year.
Y8 was a disaster. They made some quite drastic changes to the way the school was set up and it totally changed the feel of the school ( previously had single sex classes even though it was a Co Ed school)
DD suddenly experienced awful bullying from some of the boys and we realised that because DD was in the lower ability sets the classroom disruption caused by integrating boys into the class was far worse than in the higher ability sets.
DD felt very unsafe at school and her mental health suffered to the point that she needed counselling. School said the waiting list was too long to offer it to her even though they felt she was in very urgent need ( bullying triggered an eating disorder and some obsessive compulsive behaviours)
We paid for private counselling.
They had also failed to provide any of the additional academic support they were supposed to citing Covid restrictions as the reason.
We paid for private tuition.
Sadly things got worse and worse so we had to remove her and she didn't return for Y9
She is now at a non selective private school and is a different child already. Even though it's mixed teaching she says the boys are all really nice and there is no bad behaviour in the classroom. She feels safe and happy at school and can now learn in a safe environment.
I really regret not sending her private from Y7 but we had such faith in the fact that the school was rated outstanding.
We have heard of a few children in her year group also being moved to different schools. Her friend has been moved ( for similar reasons to our's) to a state school that was actually in special measures and is flying now and so much happier.