I have fond and not-so-fond memories of those clacker and/or clappers being used by various harried schoolteachers, trying in vain to keep order
You might be thinking of the "Clicker"- which was quite different than the "Clacker" aka "Clapper".
Our nuns used the clickers to signal turn left/stop/turn right/bow/sit/stand or anything else they needed to signal, such as 'stop talking'.
Our "Clacker" was a boxy looking object with a handle, which when turned with the wrist made a deep hammer-on-wood sound.
This brings back memories!
Sam