Nobody answered this, so I'll give it a shot. St. Mary's of Lynn Hockey is in the CCL (Catholic Central League), It's a competitive conference, but not as prestigious as the Catholic Conference, where you find hockey heavyweights, like Catholic Memorial, St. John's Prep, Xaverian or BC High.
Though in reality, things are changing in Mass High School Hockey. Gone are the days where the state championship was going to a Catholic Conference team every year. Matter of fact, my nephew's town school made to to the Super 8 a few years past, and were ranked #1 last season. Other town teams like Hingham and Wellesley (which have unlimited budgets due to being wealthy towns) are also competitive.
Here's last year's Division 1 rankings, you can click on a school and see which league they play in:
The official site of Massachusetts High School Hockey.
masshshockey.com