The tone of command

Ah yes voice control,

We had the year 6 to 7 day recently where the young ones come to do the selective schools test.
Well in canteen area with the evil parents milling around like a flock of starlings.
The chief examination officer was trying to get their attention and shut them up but could not make herself heard over the noise.

In my best range officers voice I screamed out "SILENCE"

What do you know they stopped?