First ignore people that shit all over BPS. There are a lot of schools in Boston, and many form opinions on headlines from the worst ones without every going, sending their kids, or knowing someone that went.

The city has a lottery system. Options are based on where you live with the exception of a common catchall schools.

Schools have different tiers inferring quality. To understand a school you should talk to neighbors. When it's time to register your kid, you will rank schools. The algorithm also considers proximity, tier, and time of registration. If your child doesn't get into their top school(s) they can be waitlisted which may open up up until and through the school year.

This process sounds scary because there is an element of chance, but I know of zero parents that registered early that did not get their kid into one of their top two schools.

This only covers Lower School admission. Upper school is another lottery, pathway, or testing admission section.

You can feel free to DM OP, I have two kids in BPS and am happy with it thus far.