Who’s at fault for not toilet/potty training the child before starting school?

My oldest wouldn't potty train until 5 and half. He finally got it down shortly before he started kindergarten. He has developmental delays- they tested for autism and its not autism they dont know why he is delayed.
He was simply diagnosed with a global developmental delay.
But trust me I tried before he was 5, it didn't click until one day it did.
It's not always the parents lack of trying is what I am trying to get at.

We only had one child in my daughters year who wasn’t toilet trained in reception that I’m aware of and he has global development delay. My own son has asd and it was hard abs we somehow managed to do it just before reception however attitudes were different then as I was told I’d need to come change him in nursery until they realised he had sen. I can’t answer if parents are responsible however I do think there should be more support from the health visitors before they start school with parents that are struggling. I also think it’s hard for parents if they work full time to find the time to toilet train.

I think unless there are underlying issues as described above by Lucy and also mentioned in OP original post then yes it's absolutely down to the parents.

I did wait to PT my boy he was 2y8m (this was due to suffering with constipation since 16m old) but I'd discussed approach with HV and GP. He was trained within 1 week we both had week off work / nursery to crack it. I've seen some where ppl say they cannot take time off but I planned and took into acc a week annual leave specifically for PT. Both myself and husband work full time

I don't get lazy parents and longer some leave it the harder it becomes to change the habit if they haven't tried due to CBA.

My daughter was potty trained at home at a year and a half. It was daycare who didnt have a potty in the classroom and told her to go in her pullup so they could change her. I had to fight to get her moved up to an older class due to her not being "old enough" luckily the teacher in that class fought for her too. But due to the teacher telling her to go so much it took another year to get her completely out of pullups during the day. Im honestly not looking forward to her going back to daycare now due to the problems I had at other others.

Yes it can be parents laziness but could also be whomever watches the child while parents are working and some kids just dont understand what they are feeling until they get a bit older

Depends on if there developmental delays, parent input. My child barely spoke before 3 and very limited understanding. We introduced a step up seat last June and encouraged him to sit on it and focussed on the language. We felt bad sending him to nursery in nappies but knew he wasn't ready. He began hating being changed so tried January didn't go well. Si blocked a long weekend off in the middle of march he was 3yrs 7mnths. So yes older and not through lack of trying. I'd say he's 90% toilet trained. Will tell us, take himself. Poos can be hit or misd but we waited till he was ready and didn't conform to pressure and judgement.
There are definitely instances where parents are at fault