If your child is happy at school, that's a pretty good reason not to mess with it unnecessarily. There's huge value in being part of your community and building social connections, especially if it's a neighbourhood school.
In thinking about whether you need to do something different, a lot of people like to start with "What a child doesn't learn" (
https://www.wku.edu/gifted/documents/resource_articles/what_a_child_doesnt_learn.pdf ). It's hugely important that our kids learn how to work hard, do hard work, fail, and persevere nonetheless. But there's lots of places other than school where they can learn this, from music, to sports, to extracurricular robotics. Same goes for their strengths and areas of passion - there are usually tons of clubs, community activities and on-line resources that enable kids to pursue areas of interest outside of school.
When is that not enough? Some common reasons include a child who is becoming more isolated - does not fit in well with their class, lacks mainstream interests (especially sports), and needs to find more like-minded peers. Some kids desperately need advanced material in their area of passion, but simply do not have the energy after a day of school to pursue as an extracurricular - they're going to get it at school or not at all. Some passions are easier to pursue in school than others, and teachers tend to be more comfortable with some topics than others (math, for example, is hard to dive into in younger grades without acceleration). For some kids, a too-easy curriculum builds perfectionism and fear of challenge.
I found that a big flag for me was when my child seemed to be a different person in certain extracurriculars vs at school (especially when teachers saw a lot of negative work habits that didn't exist in other environments). Other parents describe feeling like their child has lost their "oomph": they're not actively unhappy, but they're just kind of - - - flat.
Bottom line: ideally, we're trying to ensure our kids can feed their passions, love learning, and learn how to learn. Some kids can do this outside of school, others simply must have it in school. It depends on the mix of child, family, teachers, school, geography, district policy.... and so not only is it different for every kid, it also changes all the time.
