Images showing Millar drawing on the boy’s face were played in court and a woman, described as the driver, was seen walking past.

In a statement read to the court, the victim said she was “embarrassed” in front of her classmates.

Judge Hatton said: “It would be obvious to anyone that your conduct was appallingly inappropriate and nothing short of a cruel assault.

“You were clearly in a position of trust. One case involved drawing a penis on a student’s face.

“That involved the gratuitous degradation of your victim.”

He put two students in lock-ups and also pretended to punch and kick one of them, the court heard.