This is common, but from a kid's perspective, most would rather be sitting quietly or reading a book than doing more *work* than everyone else has to do.
You try "sitting quietly" for an hour of so in an exam room. It is just so much more fun than work, especially when it's a multi-day test - oh boy, another hour of sitting quietly tomorrow! Let me tell you, I would have gladly read the phone book if it had been an option, but outside material (even if it was only for use after the test) was never allowed in these tests when I was in high school way back in the olden days of the 1990s. In fact, I did manage to pass some time after a math test once by staring at log tables, so I imagine that a phone book would have been good for at least an hour. You were lucky if you could even get a piece of paper to doodle on in these types of tests. I remember that I was only able to get through one of them because I had a few Weird Al albums memorized, and that wore thin after two or three days. As far as I'm concerned, "sitting quietly" is nothing short of psychological abuse. And yes, I am bitter; some things just can not be forgiven.