I guess this shouldn't really surprise anybody, but a lot of the kids that think they are taking honors level classes in high school, aren't.
I don't think this is a new problem either. When I moved from MA to Kwajalein in 11th grade (over 20 years ago) I went from all honors classes at a big suburban high school, to a small DoD school. I was woefully behind on everything, and it led to one of the great comedic moments of my life.
The scene - first day in school on Kwaj, chemistry class. They are talking about moles (unit of measurement in chemistry).
Mr Taylor: Chris, are familiar with moles? Me: Furry brown critter that lives underground?
It was at that moment that I realized my honors education stateside may have been lacking something. I had the same problem with math. I had completed Algebra II in 10th grade, and was in honors pre-calculus stateside. Kwaj put me in back into Algebra II, where I had to work a lot harder than expected in what should have been a review class.
I left the DoD school system after 6th grade as the smartest kid in the class, always. When I returned to it in 10th grade, I worked harder to maintain a B average than I ever did to maintain straight A's previously. Not that I worked particularly hard for the B average, because I didn't. But I definitely fell way behind during my 3 years at a public, urban, junior high school in Panama City, FL.
I imagine the problem is much worse now.