> competition would force public schools to improve or shut down as every school vied for the vouchers.

I don't know how to fairly evaluate a school's performance. I guess we could ask if the students perform better in the job market 10-20 years later, but that's not obviously not helpful or useful information on which to make a decision now.

I get why the voucher system is appealing on first glance. After all, you often can evaluate the quality of goods and services. You can, say, estimate that a shirt you find at the mall will last a few years or that it will fall apart in a month. I just don't think you can do the same for schools. I have a feeling most people will evaluate education based on their beliefs (religious, etc) and the grades their kids "earn".