Private Middle Schools - Southern NH & Coastline

Have a child who will be entering middle school next year (grade 6). Not a big fan of the regional school and would like understand some of the better private schools in the area.

Location is in Southern NH and Massachusetts border (think Plaistow, Salem, Haverhill area).

Doesn't matter if school is in NH or MA but within 30 minutes of any of these towns is ideal. Some of the ones I have heard about is Scared Heart, Riverview, Saint Michaels).

Are there others and looking for feedback / recommendations.