But, having interviewed her, they might not have thought she would be very good at teaching secondary school maths? Again, not saying that is what happened here. Perhaps a school might decide to re-jig the maths specialists teachers so that they teach the upper years, as they thought the person they hired was a fantastic teacher and would be able to teach the lower years, plus having the extra skills they needed. Perhaps the field was weak. Again, not saying this is a good decision, but they should be allowed to make it.
Independent schools don’t have to make conventional decisions (provided they do not discriminate on the grounds of sex). It is up to those seeking an education outside of the state sector to decide whether to pay for it.