Our local PS maxes the test scores (STAR/highest state level API) every single year. Most kids are really smart and 60% or more are in pull outs for acceleration starting in 3rd grade. My child was unchallenged even with "differentiation". We pulled him out and put him in the most rigorous private school we could find and he is happier. We do loads and loads of afterschooling still.
The parents in my neighborhood think that we are crazy as everyone pays high property prices and property taxes to live there and to pay private school fees on top of that is not normal. We quickly become objects of curiosity and people flock around us to figure out what exactly was wrong with the excellent school for us to pull our son out of it. They go into data collection mode to gather any information about the school that they may have missed. They are used to being envied for sending their child to that same school.
We tell them as little as possible - but to coworkers and neighbors who are very persistent, we say that my child had behavior problems in that setting and the teachers did very little to help with those issues (true in our case - my child was bored, unchallenged and trying to entertain himself all day long with the teachers not doing much to help). That seems to make these parents happy - because we look like the parents of a kid with a problem who needed to be pulled out of the "very, very good PS".
Public school kids from my school district routinely go to the Ivies and a lot of them go to afterschool places for tutoring in academics, so most kids look really advanced. But, having volunteered in the classroom and seen how little my son was gaining in terms of intellectual stimulation, I am prepared to stay out of such a system.
PS is not ideal for a child who can learn at a faster pace than the average child.
When we met the parents with kids in the private schools, we realized that there are many who went through the same experience as us, but they don't talk about it much in a public setting.