When Charlotte-Mecklenburg Schools rolled out its post-desegregation “choice plan” almost 21 years ago, a lot of attention focused on the emergence of stratified urban and suburban schools. Suddenly majority-white suburban schools were overflowing, while urban Charlotte schools saw poverty levels spike, white enrollment plummet and many classrooms sit empty.But there was another group of schools that didn’t fit either category, schools that some called the middle ring. At places like South Mecklenburg and East Mecklenburg high schools, racial and economic diversity prevailed. But it felt like a fragile balance at the time, and it remains so.