Re: What are the chances of two dr's missing a brain tumor?
It's a good idea to have the MRI to put your mind at rest, so good for you to push it. I know of a boy whose seemed to have problems with his right leg when he was 12, and the doctors said it was a pinched nerve and sent him for physio. It progressed and they still said it wasn't much, until he couldn't use his right arm either. It was a brain tumor, diagnosed almost a year after his mother originally took him to the doctor. It's not that they miss it, it's that they don't look at symptoms and think "Brian tumor!" -- they work towards that. By insisting on the MRI, you'll move that process faster to diagnosis.
It maybe very well be that your son has nothing, but at least the MRI will show you that for sure. Keep us posted.