My only reference point is my own middle and high school experience (plus perhaps those of my classmates). From that reference point, on average, the younger teachers did a better job of actually engaging me and my classmates while simultaneously getting shafted by the school district. There were of course outliers (one or two older teachers were fantastic, and I recall at least one younger teacher who was sub-par), but "plenty" wouldn't be the quantization I'd use in either case.

It's a bit rich to accuse me of ageism when the exact problem I'm pointing out - of younger teachers getting the short end of the stick despite their skill - is literally ageism manifest.