While considerable qualitative research supports a change in the design of schools to a constructivist model of learning, there has been little research that conclusively demonstrates that constructivist, problem-based approaches are substantially superior to conventional pedagogical approaches for developing and improving student ability to solve problems and work creatively. The problem is not that quantitative research is the only acceptable indicator of quality research (notwithstanding the hegemony of structural-scientific thinking), but that the policy makers that control public education have to be persuaded to change an unwieldy beast that is the product of a century of pedagogical evolution. Bureacracies are very resistant to change and, like all organisms, are committed to nothing so much as self preservation.
The situation is further complicated by jurisdictions like Alberta that consistently rank above or very close to the top of the world in respected international assessments (e.g. the PISA program) despite a public education system that is largely conventional. [Note: The Programme for International Student Assessment (PISA)--program provides comparative information on student literacy in the content areas of reading, Math, and science from 40 OECD countries].
So the first question that emerges from a desire to compare conventional schooling to a different pedagogical approach with an eye to adopting it is...if it ain't broke, why fix it?
Regardless of the eloquence that they bring with the desire for change, innovators soon find out that the hidebound bureacrats that control education are more easily persuaded by numbers than words.