What does it take to sell a progressive, independent high school when AP and SAT scores don’t tell the whole story? And how do nontraditional middle schools – which don’t even have such data points (and can’t tally college admissions) – demonstrate their worth and success?

As schools migrate to “21st century instruction,” in which soft skills and project-based learning are foundational, accessing a school’s merit becomes more challenging to quantify. Parents debating hefty tuitions for their c...