Well, assessment will tell you what his iq is, and standardize where he is in relation to his peers, but other than give you that knowledge, it won't really do anything else.
In context, dd2 was tested half way through yr r (as I think I said, because we needed proof that she didn't have a learning disability for immigration purposes). She came out above the 99.9th centile pretty much across the board, and has (as her pediatrician likes to joke about as it's higher than his) a pretty scorching iq. In real terms, the testing showed she working between 3 and 7 years ahead of her peers.
No tightropes required. nothing changed at school. She wasn't moved up a year (no real point in moving a child away from their peers, and isolation can be tricky for bright kids if they are made to feel different or treated differently, same as any other kid), she was already being differentiated for appropriately. So as far as school were concerned, it was an interesting report to read and then stick in the file. in truth it has been useless subsequently in new situations where people are liable to fall into the 'aw, bless, what a shame' camp.
It was bloody useful for immigration though. We didn't even have to appeal, and normally with cp you have you to prove you won't be a 'burden on the state'.
Ds1 scored the highest the psych had ever tested for maths problem solving. including grad students. He was 9. We were more interested in whether the psych was able to dx asd or ADHD, although it has meant that the school have made up their mind what to do with him. They were toying with moving him up a grade overall, but the ADHD ex means that he will stay where he is. They are currently assessing him so that he can move up a grade or couple just for maths. But they were going to do that anyway, they were just waiting for any sn dx. He's now trialling some medication which is helping him get his words out. He had so much bouncing round in his head he was virtually unable to answer a question. The psych commented on the single sheet of paper he used for the 45 minutes of maths problem solving... There were just sums and scribbles and symbols covering every available surface. But he kept refusing a blank sheet. She said it was a bit like what was going on in his head.
The only one that needed a test to prove she was more able was dd1, and only from school's pov, as they couldn't enrol her on the programme without test results to show she was working over two grade levels higher than her peers across the board (a policy thing - interestingly the same policy that means dd2 was initially told she wouldn't be eligible. Having cp means her handwriting is crap )
So, there's no need to be worried. I would just sit and think about what could be improved for ds. If the answer is nothing, then it probably isn't worth it.
But assessment isn't scary. The ep will make it huge fun, and ds won't feel under any pressure to perform, it will just be a fun way to spend an afternoon. Kids at school get pulled out to go and do x with mrs y all the time, so it will be just another day at the office. 
I'm not sure why you're why you're worrying, either. I'm assuming it's because of the way most of mn treats the parents of kids who are more able. And the general distaste surrounding the g&t board in general. We're quite normal, really. And we don't even tell you iq scores unless you really want to know.
Sometimes being brighter than average causes problems, and sometimes it doesn't. It's ok to have a kid who's clever. It really is.
We just get a bit wary in here because periodically there is a bunfight and we get accused of bragging and being odious.
As suspected, There's one going on now.