I think it proves more the exception than the rule. No offence to Brockton High's achievement, but the headline oversimplifies matters. Brockton made circumstances work in its favour. It recognized that reading and writing, speaking and reasoning (in English, I assume) were the very basic fundamental skills forming the bedrock of any kind of higher learning. Thus, it insisted that every subject factored in some component of reading and writing regardless of how 'relevant' literacy in English was to the subject, even gym class. Any subject having problems implementing this odd new component got immediate support and assistance from the committee heading this initiative.
There were the usual teething problems but it worked, mostly because there was nothing further to lose anyway. The other thing was that everyone agreed to align themselves to prioritizing reading, writing, speaking and reasoning over their specific content subject area, and so allocated the necessary time and emphasis on the same during curriculum time. Needless to say, the kids got a lot of practice in these basic skills which went a long way to boosting their overall academic performance over time.
I can't imagine an already successful school pulling off such Instructional Programme alignment among their staff. Every successful Department will want to focus on it own syllabus, maintain its own reputation and see such cross-departmental cooperation as a waste of time and effort. Why risk sacrificing our good grades to help another department pull up their's?
Selfishness aside, class size may not matter if what is being taught is basic literacy and reasoning skills. Everybody teaches the same thing, everybody learns the same thing. It's teaching that caters to the lowest common denominator. But class size does begin to matter when we're teaching higher, more specialized skills and content -- when a small mistake can result in grave consequences to the final result, closer supervision is necessary.
Time to get personal. Consultation season is about to recommence. At this level, one-to-one and small group meetings are still the best form of teaching.