This is the amusing moment a resourceful schoolboy squeezed through the metal bars of a classroom window after his teacher realised she had forgotten the keys inside.

Teacher Eye Rangsiya had asked her students for help retrieving the keys left in the locked room, prompting one of her pupils to volunteer for the task in Sisaket, Thailand.

Footage shows the flexible youngster wedging himself through the narrow gap between the thin metal grills on November 26.

The boy can be seen carefully threading his legs and torso through the bars, but he became briefly stuck when his head would not easily pass through.

His classmates tried to help by gently pushing him, but they were initially unsuccessful.

Moments later, the teenager managed to slide his head through, prompting cheers from the children.

Once inside, he retrieved the keys and handed them to a classmate through the bars so they could finally open the door.