With asd and adhd diagnosed more frequently now, TA's and staff should have appropriate training to deal with and accommodate additional needs.
That being said, not all children with additional needs can cope in a mainstream school and they are better placed in a specialist school.
But ime, my ds's school had 'run out of funds' for my ds while we were applying for an EHCP. County washed their hands and said it was up to the school to be 'imaginative and responsive' to his needs and that funding doesn't come from county for my da but from the school.
Only when I told them I was seeking legal advice did additional 'emergency funds' appear from county.
The EHCP process is long and certainly in my county it seems like more staff are needed. But the end of the day the issue is No + £ = yes, and there isn't enough money
Not enough to train the staff, not enough to meet the needs of children who require equipment/additional support, not enough school places, not enough specialist schools with places available