Parental Motivations in School Choice
This paper (PDF) about what motivates parents' decisions about schools in an open enrollment district gets a little technical, but has a lot of good information about the factors at play. It explains the general concept of open enrollment and examines Colorado and Minnesota's systems in depth.
According to the researchers' findings, parents are likely to make a decision about which school their child attends based on a myriad of factors: standardized test scores, the amount of per-pupil-spending, class size, income levels, and race. However, the school districts have their own interests as well, which sometimes conflict with the desires of parents. For example, a school may be reluctant to allow special education students to transfer to a different facility because of the loss of funding they would receive. Also, the open enrollment system may be detrimental to struggling school systems, which lose funding with each student who transfers to a different school. (The paper cites Minneapolis Public Schools as an example, which lost 17 percent of its student population through the open enrollment system in the 2003-04 school year.)
This is definitely a complicated issue, and this paper, published by the National Center for the Study of Privatization in Education at Teachers College, Columbia University, is a good place to start breaking down some of the complexities.