At least four states that have made most children eligible for taxpayer-funded scholarships to private schools are seeing more families using the programs than planned. It’s especially an issue in states like Arizona and Iowa, where at least some families whose children were already in private school can now take advantage of public funding. Advocates for school choice pitch vouchers as a way to give students in low-performing schools a way out — and, increasingly, to give parents control over what their children are taught. The programs funded through vouchers, tax credits or scholarships, which have been around since the 1990s and are now available in the majority of states.