One of life's many injustices is this: that kid's with deep voices get into more trouble for talking in class than kids with higher pitch voices. I'm not basing this on any new and ground breaking research - just on my own experience on both sides of the classroom divide over the years. And its not hard to explain why, from a physics point of view.
Lower frequencies travel further through air than higher frequencies do. This is why when there are large open air concerts in the summer we can hear the bass sounds from miles away but can't hear the (higher-pitched) melodies so well, or why the sounds emanating from a nightclub seem sometimes to consist only of the low-pitched beats. In the same way a student who speaks using lower frequencies is producing a wave that will travel further and is therefore more likely to be heard - and they are therefore more likely to be reprimanded.
Why do bass sound-waves travel further? Sound waves cause the air to vibrate as they pass through, and this manifests itself as the generation of (a small amount of) heat in the air. As higher frequencies create more rapid vibrations, they create more heat energy and therefore their energy is more quickly lost to the surroundings. It's well explained here.
But here's a thing I've long found confusing: if bass sounds travel further, why is that the sounds I hear seeping out of somebody's headphone is invariably high pitched - the tsk-tsk-tsk sounds rather than the boom-boom-boom? One great explanation here is that as headphones create so little sound energy to begin with the attenuation and dissipation of that energy is not much of a factor. Instead the main issue is the frequency response of the ear: all else being equal, we hear higher frequencies better than low frequencies.
So if kids want to speak in class, they should ensure they don't have a low-pitched voice. Obviously, that's a little hard to control, so some will be left with two alternatives: keep quiet, or practise the seemingly lost art of whispering.