“…These studies have collectively provided evidence for both positive and null voucher impacts on achievement, a finding mirrored by secondary analysis of data such as those from New York City (Barnard et al, 2003;Krueger & Zhu, 2004). Additional nuance was added in the most recent evaluation of Milwaukee's program, where after five years analysts found few differences in publicprivate test scores until the last year of study, when a new public-style accountability system directed at the city's voucher schools appeared to have stimulated test score growth in that sector considerably (Witte et al, 2014). The literature is also considering non-test measures of school productivity, most notably student attainment, which new studies have shown to respond positively to voucher usage even where test score impacts are marginal or non-existent (Cowen et al, 2013;Wolf et al, 2013).…”