Hmmmm. Everyone could definitely be right, and perhaps I should be rethinking my placement for my daughter. She scored a 253 in the beginning of 5th grade this year on her NWEA MAP testing (I think that's the same test you are talking about....we usually call it, "MAP" test), which is very similar to your situation.

First thing, there are updated norms for the MAP tests, and they considerably lower the percentiles. See this link: http://www.nwea.org/sites/www.nwea.org/files/resources/NWEA_2011_RIT_Scale_Norms.pdf
A 247 in math in spring of 5th grade is 96% for 5th grade, and 91% for 6th graders, 82% for 7th graders and 76% for 8th graders. Remember that these are national norms, that include children from the lowest performing schools in the country, so if your school district is higher performing, your child would be at a much lower percentile if ranked just in your own community.

So I am not sure I would recommend skipping to the 8th grade algebra class. I'm not sure it's awful to be in the 90%+ of your classmates.

Another thing about NWEA MAP testing--somewhere I read that the accuracy drops off considerably when you get to the higher numbers. If someone gets a little lucky and answers one of the hard problems towards the end right, even if a guess, it can skew the numbers up significantly.

Yes, since you've chosen to go ahead and teach a lot of the math that is part of the curriculum, at home, he will end up doing some repetition. But it might be better for him to skip at most one grade of math, and use your time at home for other things than teaching what they will teach at school. Instead, you can focus on more interesting, non-curriculum math. Things like competition math problem solving, or special projects on cool things like Fibonacci numbers, explorations on infinity, the 4th dimension, etc, etc.

For me, with my daughter having the 253 in September of 5th grade (I assume it will be a little higher when they retest for spring numbers this month), she'll just be skipping 6th grade math, and will be doing Pre-Algebra with the 7th graders in the fall when she enters middle school as a 6th grader. As a middle schooler, there are so many new, challenging, exciting things that happen (woodshop! home ec, switching classes, puberty, new clusters, longer research papers, engineering projects, real lab science, crazy social situations, etc etc) I think it's okay to reinforce some math, and seek totally different math challenges as time permits.

Sorry, don't mean to be a downer.....by all means, no one knows your situation better than you. But I thought I'd just provide a counterpoint. No matter what you choose, I hope he enjoys it! Good luck!