A teacher at a Christian school in Melbourne's south-east has been arrested and charged with child grooming and the sexual assault of a student.

Police arrested the 42-year-old Narre Warren South man at Beaconhills College's Berwick campus on Tuesday morning.

A teacher at a Christian school in Berwick has been arrested and charged with child grooming and the sexual assault of a student.

The school told Fairfax the teacher had been arrested for indecently assaulting a child aged under 16.

The alleged conduct spans the past 12 months, police say.