The same reason that meaningful competition is usually difficult (when it is difficult)--information asymmetry. Experts don't really know what makes one school

The same reason that meaningful competition is usually difficult (when it is difficult)--information asymmetry. Experts don't really know what makes one school better than another. Is it performance on standardized test scores? Improvements on standardized test scores? College acceptance rate? Even when you do decided on a metric, one of the biggest impacts on educational outcome is parental involvement. Is school A really more effective than school B, or just more effective at attracting involved parents? If experts have a hard time judging the effectiveness of a school, most parents don't have a chance. For an example of what this looks like, take a look at for-profit colleges. Through advertising and information asymmetry they attract students who will rack up tens of thousands in student loans for mostly worthless degrees. The most successful for-profit colleges aren't the ones that are the best at educating students, they're the ones that are the best at marketing and sales.