Does your school allow subject acceleration? My DS11, when he was 8 years old and in 4th grade, scored beyond high school and into the college level in Science. The school allowed him to be subject accelerated to 7th grade that year. It made all of the difference in the world for his happiness in school.
There are many drawbacks to radical subject acceleration: homework level, writing ability and the need to write long paragraphs and lab reports, as well as social interactions. (You don't even want to know what my 10 year old came home discussing while in High School Science last year!

) There is also the danger of letting the Science curriculum outpace the Math curriculum, since you need algebra for most 9th grade physical science classes.
But so far we have been quite happy. It was enough of a jump to give him slightly more interesting material, but not overwhelm him with the drawbacks listed above.
If subject acceleration is possible, I would recommend that they give him the end of the year tests in Science for as many advanced grades as possible. You need to find the appropriate grade for him in Science.