A classic study done in the 1930’s, called the eight-year study, showed that students from what were essentially inquiry-based learning schools did better on standardized test scores, but had major improvement on intellectual competence, cultural development, practical competence, philosophy of life, character traits, emotional balance, social fitness, sensitivity to social problems, and even physical fitness.

Evaluations that measure up to the eight-year study are rare, but some relevant articles include:

• Brown, Heather (2004). Inquiry-based learning transforms the English classroom. The English Journal, 94(2), 43-48.
• Bruce, Bertram C.; Dowd, Heather; Eastburn, Darin; & D’Arcy, Cleo J. (2005). Plants, pathogens, and people: Extending the classroom to the web. Teachers College Record, 107, 1730-1753. –found improved learning in a college-level general science class.
• Edelson, D., Gordon, D. N., & Pea, R. D. (1999). Addressing the challenges of inquiry-based learning through technology and curriculum design. The Journal of the Learning Sciences, 8(3&4), 391-450.
• Prince, M., & Felder, R. (2007). The many faces of inductive teaching and learning. Journal of College Science Teaching, 36(5), 14-21.
• Spronken-Smith, R., Bullard, J. O., Ray, W, Roberts, C., & Keiffer, A. (2008). Where might sand dunes be on Mars? Engaging students through inquiry-based learning in geography. Journal of Geography in Higher Education. 32(1), 71-86.

The general story is that students seem to do about the same on short-answer tests, maybe a little better. But they do much better on the things that most of us would really value, such as independent thinking, problem solving, ability to deal with novel situations, synthesis of ideas, and creativity.