Since your DS was tested in July, his score will be compared with Fall 5th graders. There is a chart that is linked in several previous discussions on this forum so you may want to do a quick search. However, I happen to know that 251 is 99 percentile for Fall 5th grade since my DD, who is not accelerated beyond standard GT (1 year up with enrichment), scored similarly last Fall. 99 percentile is obviously very good.
However, I would submit this score only if your school does Not know that your DS has completed Algebra outside school. It is likely that your school will expect a higher score for someone who has completed Algebra or even Pre-algebra. If the school knows that your DS has completed Algebra, they may interpret this score as further support for their current position based on your DS not meeting the IQ cutoff. My conclusion is due to your school appearing to have the same philosophy regarding ability/achievement in acceleration decisions. I am not suggesting that your DS should not be accelerated, only what your school may conclude.
