I was on an Academic Pentathlon team when I was in 6th grade, which was the last year of elementary school in the area back then. It's the same principle, just fewer tests. I found that taking tests and then sitting through a lengthy awards ceremony is a pretty lousy way for an 11yo to spend a Saturday, and I turned down the invitation to join the team in junior high.
For my 9th grade year (last year of junior high back then) they introduced Quiz Bowl, some of my friends badgered me into accepting the invitation this time, and I found the experience to be a significant improvement.
In high school, the only option was Decathlon. Yeah. Thanks, but no thanks.