Vandals have caused thousands of pounds worth of damage to the swimming pool at Winslow Combined School.
Intruders have got into the heated, outdoor pool on two occasions now.
During the small hours of Sunday, September 16, up to a dozen people apparently went swimming.
In the early hours of Sunday, October 21, a group again got into the pool.
But this time they broke equipment including a pool cleaning robot worth £2,500, ripped off one of the sets of steps and left glass from broken bottles in the pool.
Headteacher Simon Rose said: “It’s just mindless. We’re very cross as a school and the pupils’ reaction was just horror.
“They love their school and they love their pool.
“We’re very lucky to have this very special resource and we do our best to maintain it.
“The police are taking it very seriously and we’re hoping they can find them.
“It’s the thoughtlessness of the damage and leaving broken glass. If my site team weren’t so on the ball, a child could have had a serious injury.”
Anyone with any information should leave a message for PC Paul Cladingboel on 101.