putting a wooden spoon can keep water from boiling over because:
Using a wooden spoon or metal does one thing, it prevents the heat build up on the center of the pot and the bottom of the pot by absorbing some of the heat, thus prevents from boiling over. The pot will boil over if the water is almost at brim of the pot. If it isn't turning the heat to a lower temp but keep on stirring to prevent that heat build up.
