Five Axies

The lecture today made sense to me more since i have a little bit of a background information on it. Seeing as my little brother has to go to the special doctors for his disability. He has a learning disability and they are always evaluating him on how he learns and how he comprehends things. They have him do different types of tasks and sees how he does each of the task they also evaluate how he completes the tasks. So when it was said that they dont diagnose little kids with things since they are so young how do they know if it all stay or will the disorder go away after time?