A head teacher attacked his deputy with a wrench after being hit by "overwhelming sexual jealousy" due to a love triangle at the school.
Anthony Felton, 54, admitted attempted grievous bodily harm with intent after the attack at St Joseph's Roman Catholic Comprehensive in Aberavon, Neath Port Talbot, on 5 March.
Richard Pyke, 51, was treated for minor injuries in hospital after Felton sought him out and attacked him from behind.
Felton, of Penyrheol Road, Gorseinon, Swansea, was sentenced to two years and four months on Friday and Judge Paul Thomas KC said he suspected a head teacher attacking his deputy was "entirely without precedent".