Okay, you know what she literally said. But what those kids heard was that if they didn't behave they would have to read for punishment. Punishment? Reading should be a reward as in... "If you walk nicely to the cafeteria for lunch, I'll let you read silently for the rest of the day...the week...the year...!"
And while we're at it, let's stop making our athletes run laps when they lose a game or run a drill incorrectly at practice. Exercise - another activity we want our children to choose - but they won't if they "hear" it as punishment.