This caution abyt Russ Whitehurst is relevant as we consider public support of pre-K in New Hampshire:

“Generalizations to state pre-K programs from research findings on Perry and Abecedarian are prodigious leaps of faith,” wrote Grover J. “Russ” Whitehurst, director of the Brown Center on Education Policy at the Brookings Institution, last month. “Perry and Abecedarian were multi-year intensive interventions whereas state pre-K programs are overwhelmingly one-year programs for four-year-olds.” He also noted that today’s students face different the circumstances than those of 30 to 40 years ago.  

more: Obama and early childhood education: a rhetorical leap of faith – The Washington Post.