What sort of person/dr is doing the assessment? What tests/tools will they be using?
The neuropsych we took our DS to had us and DS's teachers fill out several forms about his behavior, skills, emotions, etc, etc. She administered the WISC and WIAT and he was observed the entire time. To evaluate him/diagnose him, all the information was taken into consideration - the forms, his test performance, his behavior/emotions during the test, his body movements, the way he spoke - basically EVERYTHING! Then, using all those years of schooling/training/experience she arrives at a diagnosis and she explained to use WHY she diagnosed those things.
Now, not every assessment is going to result in a diagnosis... sometimes they can't be sure... sometimes kids are borderline and one dr might see something where another dr doesn't. Sometimes the kids won't play ball at all, and you get nowhere.
This is why it's stressed on here to find an assessor who has experience dealing with 2e kids!