The Ontario Ministry of Education recently released their study on the efficacy of full day Kindergarten. For those who are interested it is a fascinating read. It's over 200 pages long, if you don't want to read the whole thing I recommend looking at the Results section and the Conclusion and Recommendations section. It says fall 2012 on the cover of the study, but to the best of my knowledge it was made available on the Ministry website in October 2013.
http://www.edu.gov.on.ca/kindergarten/FDELK_ReportFall2012.pdf