A new study from the Center on Education Policy looks at 10 years of data, concluding that despite the claims of advocates, school voucher programs have not had a positive impact on student achievement. As a result, proponents have had to shift their rationale:

With the publication of more recent evidence showing no clear achievement advantage among students receiving publicly funded vouchers, the rhetoric used to justify vouchers has shifted. Although some voucher advocates continue to maintain that vouchers have been found to improve student achievement, others note that vouchers have not been found to harm the achievement of participating students…

Educational value has been one of the primary excuses used by voucher advocates to justify the church-state dangers of sending taxpayer money to religious institutions with no assurance of constitutional safeguards. Ten years of study later, there are no educational reasons worth risking the threat to religious liberty posed by such funding. 

The 57-page report analyzes ten years of data from prior voucher studies, reviews current voucher programs, and outlines the current  landscape of court cases and ballot initiatives relating to vouchers.