The NYT now has an article on this, mostly about ability grouping by a teacher within a classroom, rather than assigning different ability groups to different teachers at the same grade level.

http://www.nytimes.com/2013/06/10/e...bility-regains-favor-with-educators.html
Grouping Students by Ability Regains Favor in Classroom
By VIVIAN YEE
New York Times
June 9, 2013