If you live close enough to your child's school to walk there, that is always the best choice. Fresh air and exercise are always great for you.
Sometimes you don't have that option, and have to drive them to school. If you drive your child to school and have to wait for them to be allowed into school, turn your car off as soon as you park.
1. You won't pollute the air with toxic fumes.
2. The people behind you with children in their car or with respiratory issues will not be forced to breathe in your fumes - neither will your child when they approach the cars, they are right at the level where the fumes exit your car!
3. You won't waste your gas.