This isn't good parenting. "Please make my kid walk in bone chilling cold weather in nothing but school issued shorts and shirt, while I am perfectly warm and don't have to worry about it."
No one has said anything about just wearing shorts and shirts.. Additionally, schools have rules as to how cold it has to be in order to stop PE, which they are of course following. This IS good parenting.
You shouldn't be able to miss gym class just because you think it's cold. Unless you have an illness or a special condition or it is just do that cold, you should be able to go with all the other students to go outside
We were a bit quick to judge