Others have said it, but I want to emphasize that you're asking this question at the *perfect* time. The JK/K lottery is this month and only this month! (Well, you can register later, but you have less choice.) Act now!

Also - the CPSD site has recordings of Zoom information sessions explaining the lottery. Might be helpful.

Also also - Cambridge is full of excellent elementary schools. You're unlikely to make a wrong choice.