Hearing loss for musicians is usually the result of either being exposed to loud sounds for extended periods of time or from short, but very loud exposures. Both of those can happen at any time on a stage, in a studio or while practicing, and for drummers, the risk may be higher than for the other musicians. Cymbals and snare drums are inherently loud, especially since their purpose is to cut through the sound of the other instruments for rhythmic and emotional effect. The effects of not protecting your ears can be devastating in the long run.  Drummers need to be extremely cautious as most full-sized drum kits are known to produce between 90 and 130 decibels of sound.  The higher dBs are typically from snare drums and cymbals which are the things that drummers usually hit the hardest.  Many drummers suffer from tinnitus, which was caused by exposure to loud noise.

Because of the long term effects on your hearing, the directors recommend the following protection that limits the harmful sounds, while allowing the students to still hear the music around them.

Options:
Etymotic Research ER-20XS High Fidelity Earplugs - Universal Fit ~$25
High-fidelity Earplugs with 20dB of Sound Reduction, Carrying Case, and Removable Neck Cord - Universal Size
https://www.sweetwater.com/store/detail/ER20XUniv--etymotic-research-er-20xs-high-fidelity-earplugs-universal-fit
 
Vibes Hi-Fidelity Earplugs - Universal Fit - ~$30
High-fidelity Earplugs with 22dB of Sound Reduction, 3 Eartip Sizes, and Carrying Case
https://www.sweetwater.com/store/detail/VibesEarplug--vibes-hi-fidelity-earplugs-universal-fit
 
Vic Firth VICEARPLUG High-Fidelity Hearing Protection- Regular Size -~$20
20db sound reduction across all frequencies, Standard fit, Includes heavy-duty neck cord and carrying case
https://www.amazon.com/Vic-Firth-High-Fidelity-Earplugs-VICEARPLUGR/dp/B00AL2UDZ4?dplnkId=1bc2d3e0-1d5c-46fc-9370-837822de3515&nodl=1