Has guidance changed for high schools with regards to isolating?

[And48]

I've searched online and can't find anything concrete that explains this.

My son has a cough which started last night and generally feels unwell. He is highschool age. I spoke with his school this morning and they have said that if his lateral flow test is negative (which it was) then he can go to school. He doesn't need a negative PCR test.

I kept him off and booked a PCR which school have said is unessessary. This isn't how I understood things, am I wrong?

They are wrong, you are right. Symptoms = PCR.

Unless your school is part of the pilot test that has been happening, symptoms = isolate + PCR, so you are correct.