I read it here:
http://www.edweek.org/ew/articles/2...njBIYKUnyJWwbRq7iHeln&cmp=clp-edweek

One thing that surprised me was this:
The NBER researchers did not describe in detail the curriculum or specific services of the district�s gifted programs, but district officials reported that their gifted and talented programs focused on exposing students to more in-depth discussions of grade-level topics, known as an enrichment approach, rather than acceleration, or moving through existing material faster and adding new topics.