The headmaster had just spoken to the naughty students. They misbehaved again.

Had it not been for the naughty students’ misbehaviours, the headmaster would have spoken to them.

Not until the naughty students misbehaved again did the headmaster speak to them.

Hardly had the headmaster spoken to the naughty students when they misbehaved again.

Only after the naughty students misbehaved again did the headmaster speak to them.