Laura,
If you think your DS should get >433, ask him if he was satisfied with the test. When my DD asked me what she got for her score and later she said, she did not know the time was running out and she missed 6-7 questions. She wanted to take it again (she hates it when she score <90 on anything).
Your DS might not have finished the questions as well. If that's the case, he can retake it. (JHU name has a lot of weight and easier for advocacy, in my case at least). Otherwise, formal IQ testing will be good but the principal will weigh in his teacher's recommendation as well.
In our school district, we have IQ testing for students nominated for TAG and they already know who has high IQ anyway and another IQ test won't change their mind.
We have 4 other kids in my DD's class who are ahead in their class and my mission for this fall is to organize them and get CTY or EPGY online class for them while other kids do regular class. You may want to check where his classmates LOG are and may be easier to advocate along with other parents.
