One of the things that I notice teaching and working with both MS and HS students, is the change that happens from MS to HS- between grade 8-9th grade in terms of excitement for learning. 8th graders are excited about learning and trying new things. But when they become 9th graders they are not nearly as excited. The change is instantaneous. Why? In my opinion, HS students and 9th graders, understand that there are 4 years of high-stakes grading that goes on transcripts to colleges. Teachers are not as warm and fuzzy and expectations are higher at home and school. It is now time to jump through hoops, where everything counts towards that GPA and life after college.... They lose sleep, and get increasingly stressed out to the detriment of mental and physical health.
Now, some schools are taking it upon themselves to change that culture. This article from Inside Higher Ed, talks about some top private high schools that are trying to change that culture.