The RAF shy away from this as the individual has to be regarded as a 'member of staff' for insurance purposes and H&S@W. These comments are based upon experience trying to get ATC Cadets work experience for one day.
Bolleaux to the latter. 28 and 33 Sqns manage to take 15 y/o work experience trainees every year. My daughter did so last year - she's in the ATC, but it was set up by her school direct with Benson, without the ATC Sqn's input. They had three others there at the same time who had no ATC background. I could find out who set it up at the light blue end if that would help.