My kid is in HS, but I can share for us, the middle school did a very good job preparing them for a rigorous HS experience. Math and English classes in the MS are very small and because split the main class into three smaller classes based on level with groups as small as under 10. So in eighth grade some are doing Geometry and some are doing Algebra. I believe one year they accommodated one student who was in Algebra II in 8th grade.
They have a strong science program where all MS students have a science fair every year and are guided through the process of doing the research, experiments, and presentation of results. That was a very good experience for my kid and it helped them in HS with science projects.
The only downside I can share is that it is a very small school with only one class per grade. In middle school, that means your student will not have a lot of options socially and it might be too limiting. It was fine for mine though.