A new study out of Vanderbilt University has some surprising findings: children from low-income families benefit significantly from Tennessee's pre-kindergarten programs at first, but those gains wear off by the end of third grade. Researchers also found that students who did not attend pre-K quickly caught up to the students who did attend pre-K.

The study raises questions about the efficacy of Tennessee's pre-K programs, which were widely expanded in 2005. Dale Farran, a professor at Vanderbilt and co-investigator of the study, discusses the findings with Here & Now's Jeremy Hobson.