Matthew Ladner:

I believe that open enrollment is a big reason that Arizona has been leading the nation in NAEP gains, and that charter and private choice programs deserve some credit the eagerness with which districts participate. Take a look at Columbus on the above map- a large urban district literally surrounded by districts choosing not to allow open enrollment transfers. Now take a look at the school district map of Pima County. The Tucson Unified School District is surrounded by districts that do participate in open-enrollment- actively.

Much more on open enrollment, here.