Oh, I am sorry if I was unclear. His entire class is moving from 8th to 9th grade. It is rather silly that they have a ceremony for it (they never did when I was in school), as it isn't a significant achievement (everyone moves from 8th to 9th grade!). But since they move schools and will be attending the high school next year, they make a big deal out of it. DS2 is not skipping a grade, although he is on track to take AP level courses in high school.
Schools in the US, generally speaking, are VERY hesitant to hold students back or to promote them ahead of their normal year in school. Studies when this was more commonly done in the past indicate that social development is as important as academic, and artificially promoting or holding back a student can cause bigger issues than previously thought. It is still sometimes done, but our school has not done this in years, regardless of test scores.
Indeed, while I handle the test scores for our school, and my children are in the top few, they are not usually the highest scoring students. Sometimes they are, but not consistently. Even so, I will take it. They're above average to me!