Remove the water containers to a safe place. Have the children strike the fork again. Have them repeat the process, this time putting their ears down on the table. All things are made up of molecules. The molecules in solids like metal or wood are tightly packed together and they can carry sound waves more efficiently than the spread-out molecules in air.
Solids are good transmitters of sound.
Sound travels through steel 15 times faster than through air. Let some children choose a new site to place their vibrating forks. If your school has a metal hallway railing, you may use it to prove that sound travels better through the metal than the air. Space your students along the railing- the longer the rail, the better. Have someone at the front of the line tap a tuning fork and hold it in the air.