For best results have the children sit in a circle. 

Choose one player to hide their eyes or leave the room so they can not see.  

The teacher then quietly chooses one person to be the leader.

This player then starts make some sort of movement.  This movement can be waiving, patting their head, rubbing their belly, whatever the kid wants to do as long as it is done within the confines of their seat.  

Every other player will mimic the leader.  The player chosen to be it can now reenter the room or uncover their eyes.  It has 3 guesses as to who the leader is.

The leader should change movements occasionally and other players must follow along.  Advise the leader that movements that make sounds such as clapping or snapping can easily give them away as they will obviously be the first person to start making the noise. Repeat with a new It and new leader.