When you are distressed or in a crisis you often choose to act or think in a way that makes your situation worse. If you can distract yourself for a short time you can choose to act more wisely. For example, if you had an argument with your brother on the way to school, you left your phone at home, and your Mum told you off for not doing your chores - all before you had even arrived at school. Then your teacher handed back your assignment with a big, fat 'F' on in. You may be tempted to scream, cry, punch a wall, throw something or storm out.
If you can distract yourself, you are less likely to act on the emotions that you're experiencing. It might be difficult in the classroom setting as given above, but here are some options: