A security firm has told the Herald it is illegal to pat down students - even at a school ball.

Elton Rangi, founder of Artus Group, was appalled to hear students attending Wesley College's school ball on Saturday were patted down, with girls reportedly having to expose their upper thighs before they were allowed in.

A legal expert has also questioned the way students were searched but stopped short of saying it was illegal.

A 17-year-old student who attended the ball at Auckland's Ellerslie Event Centre said girls were herded one by one into a room and searched by a