If the children are still working at P scale levels, they are developmentally so far behind KS3 that I can not see how they will be able to access the mainstream curriculum. It’s unfair on them, the teachers and their peers. Might also be useful to have the parents involved – especially if they understand that the mainstream curriculum is well beyond needs. I’m guessing you will just see behaviour – either shut down / zoning out or disruption as the learning is so far away from their ability.