Don't the Cornwall schools guidelines go against the DfE's own current guidance?
Yes. It's absolutely baffling that the DfE is siding with the school in this case. Their own guidelines published in 2020 make it quite clear, for example, that schools shouldn't teach children that it's possible to be born in the wrong body.
The other thing, of course, is that the Cornwall guidelines (which I assume are based on the Allsorts transgender toolkit adopted by local authorities) are quite clearly in breach of equality legislation. Oxfordshire local authority dropped its use of the toolkit when threatened with legal action by a teenage girl, and a number of other local authorities followed suit.
Finally, as others have pointed out, thanks to the Forstater ruling, gender critical beliefs are now protected in law. It's interesting that the parents' case is based on the Equality Act's inclusion of religious belief as a protected identity, but possibly this case was launched before the Forstater ruling.