The offences are in sections 16 to 19 of the Sexual Offences Act 2003, with the positions of trust defined in sections 21 and 22. One of those positions is looking after under-18s who are receiving education at an educational institution where the young person is also a pupil or student.
KCSIE 2026 reminds schools of this when writing the staff behaviour policy, or code of conduct (paragraph 123 and footnote 29). It points out that the position of trust can apply to staff who don't teach the child, as long as they look after under-18s in the same school or college. A sixth-former aged 16 or 17 is protected, even though they are over the age of consent.
The 2022 extension. The Police, Crime, Sentencing and Courts Act 2022 added section 22A, in force from 28 June 2022. It extends positions of trust to people who regularly coach, teach, train, supervise or instruct a young person in a sport or a religion. That matters for schools working with clubs, coaches and faith groups, including through lettings and extra-curricular activities.
A concern that a member of staff is in, or grooming towards, a relationship with a pupil meets the harm threshold and should go to the LADO. Staff codes of conduct usually also cover boundaries, such as private messaging with pupils.