Glyn Knowles, 50, who was acting head of Cambridge International School, was caught in a sting by an undercover journalist posing as a teenager.
admitting a grooming charge.
He then turned the conversation to sex and sent the boy a picture of himself in his underwear, asking him intimate questions.
They arranged to meet in Bishop’s Stortford but the journalist informed Hertfordshire Police of the meeting, and Knowles was intercepted on 14 July.
Sentencing Knowles, Judge Andrew Bright QC said: “You were responsible for the protection of children, not the abuse of children.” Knowles was handed a 12 month prison sentence which he will serve six months behind bars and a further six months out on licence.