"Visible Learning: A synthesis of over 800 meta-analyses relating to achievement. ...a culmination of 15 years of research incorporating more than 50,000 studies and over 800 meta-analyses involving millions of students and represents the largest collection of evidence-based research into what actually works in schools to improve learning."

Am interested if anyone has found similar meta-studies related to gifted.

Hattie's writing style is somewhat cramped, and his preface and early chapters were disappointing, but in the end, the sheer scale of the work, and some of the conclusions it draws, are intriguing and far-reaching. At the very least, its a vital reference for different factors affecting learning, and one can go straight to the appendix and the footnotes if they have any issues.

https://www.eduweb.vic.gov.au/eduli...ubl/Researcharticle_visible_learning.pdf

http://lib.freescienceengineering.org/view.php?id=544851 (summarized in Appendix B)

http://www.amazon.com/Visible-Learning-Synthesis-Meta-Analyses-Achievement/dp/0415476186