One of the constant refrains from the teachers unions is that vouchers don't do anything for kids.

But two separate studies of voucher-using students in Indiana and Louisiana should be encouraging for school choice advocates.  

Interestingly, both studies found the same phenomenon: students do worse initially in their new school and then  their performances take off.  A Wall Street Journal editorial describes what happened in Indiana:

[R]esearchers Mark Berends and R. Joseph Waddington focused on Indiana’s statewide voucher program that now serves more than 34,000 students. The study found that students using vouchers had declines in math and English for the first two years after leaving public school. But the longer these voucher kids stuck around in their new schools, the better they did—surpassing their public school peers in English after four years.

The Louisiana findings are similar:

Today 7,100 [Louisiana] students—nearly 90% of them African American—attend private or religious schools of their parents’ choice thanks to a statewide program that includes vouchers for private schools. In February 2016, Jonathan Mills of Tulane and Patrick Wolf of the University of Arkansas released a study that found declines in English and math after two years at a private school using a voucher.

But that wasn’t the end of the story. Messrs. Mills and Wolf expanded their study to include performance after three years, and when they did the results flipped. Their new study shows that, by the end of the third year, the differences between voucher students and those in public schools had been erased.

The explanation for this is probably a commonsense one:

Student improvement after the first two years at a new school is also consistent with common sense. Parents and teachers know that changing schools can be a big adjustment for children, and private schools typically have different cultural mores and teaching habits. Most parents don’t look for private schools if their children are prospering in their current school.

Teacher unions are likely to point out that in the Louisiana study the differences between public school students and voucher students were erased rather than surpassed at the end of the third year. This points to the need for long-term studies and overlooks other important factors such as safety and the culture of a school. It also overlooks parental preference. As the Wall Street Journal concludes:

Even if test scores aren’t notably different, why should the default be keeping kids trapped in public schools rather than letting parents make the choice?

These new studies should give a boost to those who believe accountability comes from parents who know better than a distant education bureaucracy what schools best work for their children.