A few years ago SB5 with 139 score, level 3 according to Ruf. According to the report, he is able to handle reading-based and mathematical materials three to four grade levels successfully...
Wow!
I wouldn't worry about Iowa acceleration scale at this point it's moot. The only keys that apply to your situation is -
1) Will it crush 6th grade sibling if younger brother is taking high school or middle school classes?
2) Does your 5th grader want a full grade skip? As Catalan says - if he is totally set against it, then you may need to ease into the full skip or work around it all together.
3) Can he type? Efficiently?
My next question is to pull out the report and look: Was it 18 months ago or 4 years ago? It doesn't really matter, but it's one thing to say that a 1st grader can do 5th grade Math, and a totally different thing to say that a 5th grader can do 9th grade Math.
I would then call the tester and outline the situation, including 6th grade sibling, and get professional recommendation. It's ok if you mess up and have to rearrange things, but it's better if you don't.
The next thing to look at is logistics. Is the high school near your son's current school. Is it closer to the middle school? Then you have to think about grades. High school grades 'count' on the college application so your son had better be ready to type 6 page papers or whatever the honors 9th grade English or History kids do before he gets those classes on his transcripts. He could perhaps 'audit' 9th grade English and History and be given credit "Pass" for 5th grade English and History.
It's idea if you have a friend who saves lots of her kid's work who is in 8th and 9th grade so you can get a good eyeball at both the syllabus AND the level of writing expected of kids at that level.
Being able to think about 9th grade level ideas and being able to communicate about them -when the grades count - are two different things. If I had the freedom to choose for my son, I would have had him audit 9th grade English and History as a 5th grader, audit 10th grade as a 6th grader, etc, and then do 9th grade 'for real' when he got to chronological 9th grade. But my son has ADHD, so even though he's also Ruf Level 3, getting it down on paper at the 'A' level is a whole different struggle.
If they don't buy the 'Audit' plan, a reasonable compromise plan is for your son to do Math, English and History in 8th grade with hand-selected teachers, so that your 5th grader can still be called a slimy 5th grader by big brother, and next year 5th grader can be out of the building in time for 6th grader to enter. I think it's really sad that boys self worth and status is so tied up in their grade level, but it's a reality for many kids. That way 5th grader has a chance to deal with the increased product requirements before he hits 'grades that count.'
For some families high school grades aren't as much of an issue, but I couldn't deal with closing off 'certian options' because I was sending in a young kid to deal with big kid levels of homework. Other level 3 kids are better at reading social cues, and have no problem getting As 3 to 4 grade levels up.
Aside: In some schools '8th grade Math' has a lot of options: Basic Math, PreAlgebra, Algebra 1, Geometry. They will have end of year tests that will help determine where your son is. If getting the 5th grader out of the building before the 6th grader gets there isn't an issue, you have more flexability. My son went from finishing 4th grade Math to Honors 7th grade Pre-Algebra with no Hothousing or preperation. After 3 months we brought him back to 6th grade Math because he just wasn't getting the Pre-Algebra and it was a logistics nightmare. The next year he did the Honors 7th grade Pre-Algebra and had a wonderful year. Same teacher, same textbook - and none of his famous 'class clown' behavior. It makes me smile just to think about it.
Love and More Love,
Grinity