Police are talking to a Taupo boy and his family after the child brought a grenade to his intermediate school, sparking its evacuation.

Taupo Intermediate School staff called police about 11.50am today, and students were evacuated into the middle of the field, where they waited for about two hours for the all-clear to be given.

The army bomb squad arrived at the school about 2.10pm, finding the grenade to be missing its detonator.

"Other than that, it looked like the genuine article," Taupo acting Senior Sergeant Stuart Duncan told NZPA.

He commended the school's staff on their dealing with the situation. Officers were talking to the boy and his family to find out where the weapon came from and why he had it, Mr Duncan said.

"He is back in the care of his family, with police inquiries continuing as to why the child thought it was a good idea to bring it to school."