If I remember correctly, its complicated as there are three primary towns involved (Prospect, Beacon Falls, and Oxford), a lot of egos involved and some cultural and budget conflicts. In the early '90's, Prospect sent their kids to Naugatuck and Wolcott high schools. Beacon Falls sent their kids to Naugatuck and Seymour high schools and Oxford sent their kids to Seymour and Masuk high schools.
Int he early 90's, Prospect and Oxford (along with Wolcott) were growing noticeably while Beacons Falls was not. Oxford's growth also involved a cultural element that was not rooted in the old Valley. Naugatuck was facing revenue issues, i.e. taxes, due to loss to manufacturing in the area. Seymour had the same issues, though to a lesser degree; but, they also had serious issues trying to pass school budgets, which is still a challenge for them today. So, both Seymour and Naugatuck high schools' were falling apart and over-crowded due to increasing enrollment for these feeder towns.
By the mid 90's Wolcott told Prospect that it could no longer take all of the Prospect students that wanted to go there and Naugatuck HS was falling apart. Seymour tried to renovate Seymour HS; but, tried to pass most of the cost to Beacon Falls and Oxford. That got Beacon Falls to ask Oxford to form a regional high school, which made sense as they are adjoining towns. Oxford said no and many felt it was a big NO to the Valley. With a common link (Naugatuck HS) and a common need, that led Beacon Falls to partner with Prospect to form a new regional high school that became Woodland and opened in 2001 (I wonder how much fun school bus rides are from Prospect to Beacon Falls along Route 42 in the winter when it snows, likely as much fun navigating around Route 34 across the Stevenson Dam between Oxford and Monroe in the same weather). Needles to say, Woodland did not offer to take in Oxford kids.
Oxford, which kept growing, then formed a second partnership with Pomperaug. The problem there was that both Southbury (Pomperaug) and Monroe (Masuk) where also growing and could not manage all of Oxford's students. Thus, in 2007, Oxford built its own high school.
As a FYI, current enrollment of the impacted schools:
- Masuk (Monroe): 1,100
- Nagatuck: 1,200
- Oxford: 600
- Pomperaug Regional: 1,200
- Seymour: 700
- Wolcott: 800
- Woodland Regional: 700