The No Child Left Behind Act of 2001 (NCLB, 2002) has had a great impact on states' policies in assessing English language learner (ELL) students. The legislation requires states to develop or adopt sound assessments in order to validly measure the ELL students' English language proficiency, as well as content knowledge and skills. While states have moved rapidly to meet these requirements, they face challenges to validate their current assessment and accountability systems for ELL students, partly due to the lack of resources. Considering the significant role of assessment in guiding decisions about organizations and individuals, validity is a paramount concern. In light of this, we reviewed the current literature and policy regarding ELL assessment in order to inform practitioners of the key issues to consider in their validation process. Drawn from our review of literature and practice, we developed a set of guidelines and recommendations for practitioners to use as a resource to improve their ELL assessment systems. The present report is the last component of the series, providing recommendations for state policy and practice in assessing ELL students. It also discusses areas for future research and development. (Contains 3 figures.) [The work reported in this document was supported under the National Research and Development Centers, as administered by the U.S. Department of Education's Institute of Education Sciences. For parts 1 and 2 of this report, see ED502283 and ED502284.]