Selection bias. If your parents care enough to send you somewhere, they'll care enough to make you do your homework.
"The evaluation is based on a randomized controlled trial design that compares the outcomes of eligible applicants randomly assigned to receive (treatment group) or not receive (control group) a scholarship through a series of lotteries."
Now, given lottery status parents might help their kids with HW or otherwise (b/c they don't want to waste an opportunity). I am still reading on how they control for that, but I suspect they have a TON of observables on the parents, income, location, etc. School voucher studies these days -- particularly those read and "approved" by those in the list of acknowledgements -- will go nowhere without either randomization or a suitable instrumental variable that correlates with the voucher, but not with educational outcomes. No need to throw around econometric criticisms until you read at least part of the article.
Another factoid that Cato likes to throw out is that public education spending has doubled on an inflation adjusted basis since the early '80s, yet scores on certain standardized tests have stayed constant. Still, listen to any presidential debate. Every candidate calls for more money for schools, more teachers, more computers, etc. It doesn't occur to them that the system is broken when scaling up the input produces no additional output.
http://www.heritage.org/research/Education/images/b2179_char...
Same performance as (presumably) measured by one standardized reading test and one standardized math test...
http://www.cato-at-liberty.org/2009/03/17/american-prospect-...
When you add that a priori economic reasoning is firmly on the side of school choice over public monopoly - well I'm convinced. I'm a little surprised popular wisdom isn't on my side.
That's like saying "well wikipedia didn't exist when I was a kid and I turned out just fine" to argue that Wikipedia should be banned -- after all voucher proponents don't want vouchers to be mandatory, just optional!
Editing to add more detail:
Based on my reading, they're spending more then $300 million on special education, around 25% of their budget.
$62 million goes to the university $46 million goes to the public libraries ~$100 goes to early education and ESL initiatives.
Those are all expenses private schools never have to worry about.
But suppose it is correct. Do you think parents might start caring more about managing their kids' educations if they could see that caring more actually made a difference?
That statement may or may not be true. It's simply speculative. It also seems specious to me. Making a commitment for an hour or two that involves signing a couple of papers is nowhere near the level of making a commitment to follow and monitor schoolwork.
One great example is this: I never cared about china patterns until I got engaged and was asked which one I preferred. Suddenly I had all sorts of strong opinions.
With vouchers people would start caring a lot more about what they were getting, and schools would have to frame their role less as daycare and more as a value proposition... as in "come to school A and our research shows you will earn $10K more per year after college", or "our students learn three languages fluently during grades 6-10", or "we offer all vegan food and teach set theory before algebra, and 50% of our students end up majoring in math in college".
Is measuring merit all that hard? It's done successfully higher ed. The bottom line is that we shouldn't worry so much about the concept of merit b/c we don't need a one-size-fits-all system. For example, some people prefer to go to a large public university where profs are "meritorious" if they publish and are at the cutting edge of research -- while others prefer to go to smaller schools with more of a focus on teaching and small class sizes.
Chances are with widespread voucher availability, K-12 education would become less cookie-cutter and would better address the diverse definitions of merit that exist.
Of course, states/cities could require certain curriculum, teacher SAT scores, etc., but such things would represent a floor rather than a ceiling on what "merit" is.
I would let the learners have power to shop, and we will know soon enough which teachers are doing a good job.
Market based: If the student didn't use the voucher but might use it next year, then the school will try harder to meet the student's needs this year.
Psychological: If you perceive something as simply mandatory, you will take it for granted. While if you had a voucher and choose a public school, then you have made the decision that you have the best opportunity in the environment you chose, and you'll try to extract value from it.
The idea that parents should be able to choose where their children go to school should be a given in America. I understand and accept everyone paying into the education system as a good idea, I don't understand or accept that people with school aged children have to pay into the school system even when they have chosen to send their children to private schools.