A child refuses to put shoes on, argues over every instruction, shouts when asked to start homework, or suddenly bolts from the classroom. In those moments, it is understandable to wonder whether you are seeing a stress response vs defiance.
An adult snaps at work, forgets simple things, or feels constantly on edge. A child melts down over homework they could do yesterday. A student who is usually capable starts refusing tasks, fidgeting, or lashing out. When this happens...
A child can know their spelling words at home, then freeze in class and forget every one of them. An adult can read the same email three times and still not take it in. That is often the moment people ask, why does stress affect learning?