I'm probably the only parent here who has experienced waldorf in the upper grades and high school. I went to a waldorf school from the middle of 8th grade to the middle of 10th. My daughter attended from preschool through HS with a break in the middle: half of 8th in a public school and then 1 1/2 years of homeschooling.
After my two years of waldorf I went back to a public HS. My brother "marked my card" (totally illegally) and got me into the honors program. I had no difficulty getting straight A's. Many years later, when I finally got around to going to college, I again had no problem getting straight A's, except in Ancient Greek (I'm not good at languages). I think my two years of waldorf made a huge difference in my academic career. In public school, things were taught in small boxes. Math over here, literature over there, history in another space. And even within subjects, connections were frequently not made. Of course this was in the 50's and early 60's. Perhaps there has been some improvement?
To give a concrete example, in American history we learn about the French and Indian War. It wasn't until I was a grown-up that I figured that this was actually part of the Seven Years War, a huge struggle between the French and English for world domination, with battles in India, Europe, all over the high seas and a few unimportant skirmishes in North America. At that point, the English desire to get the colonies to pay for their own part of the war made sense: the English were broke after fighting a all over the world for seven years.
Anyway, the waldorf approach of linking ideas together and teaching across subjects was very exciting and opened up my thinking. It is exactly the sort of approach that college level profs like. If you can write papers that link and connect and show real thinking you get better grades. Trouble is, many years memorization and multiple choice tests are not good prep.
My daughter took a couple of years off after high school before going to college. She eventually completed a degree environmental engineering, specializing in water quality, especially surface water. If you want to make a joke of it, you could say that she is an expert on mud puddles! She did very well in college, getting high grades while working two or three jobs (I was in college at the same time, so she had to support herself). I asked her if waldorf had helped or hindered. She felt that it had helped her cope with college level work in several ways:
1)She knew how to do things from scratch and was interested in really getting down to the core ideas, rather than just memorizing enough to pass the tests
2)She was self-confident and iconoclastic, willing to argue against or for almost anything in the process of learning
3)Her ability to visualize in 3 dimensions, to draw, etc., all proved to be useful for advanced math courses and engineering courses
4)Her HS had required lots of paper writing, so she was well-prepared for college level work.
5)In a waldorf HS a full range of science courses is required: she had physics, chemistry, mechanics, biology, botany and more
Anyway, I think I've said enough. I would like to point out that waldorf schools vary lot and not all waldorf schools would provide as good a foundation as this one did. Ask questions, look at the teachers qualifications, check out the main lesson books, etc.
Just one more thought: my daughter has her daughter in waldorf already, so I think you could say that she is very happy with her educational experience!