A school which admits only boys is not discriminating unlawfully against girls.
If the daughters of certain members of staff at a boys’ school are allowed to attend, it is still regarded as a single-sex school.
A boys’ school which admits some girls to the Sixth Form, or which lets girls attend for a particular GCSE course not offered at their own school is still regarded as a single-sex school.
A boys’ school which admits girls to A-level science classes is not discriminating unlawfully if it refuses to admit them to A-level media studies or maths classes.
A boys’ school which admits girls to the Sixth Form but refuses to let them use the same cafeteria or go on the same visits as other Sixth Form pupils would be discriminating unlawfully against them.