Taking a look at the research on Pre-K

The Hechinger Report: “Does Pre-K really help?”
The Hechinger Report Does Pre-K really help? http://hechingerreport.org/content/pre-k-really-help_15406/

The Hechinger Report has a roundup here of the research on the effectiveness of Pre-K. It's a good refresher as more cities and states carve out funding for early education -- most notably here in New York City, where Mayor Bill de Blasio and Governor Andrew Cuomo have pushed to make Pre-K available to all of the city's public school students.

The big caveat here, as always, is this: It's all about the quality of implementation. Making Pre-K available is step 1. Step 2 is making it work.