This report by the Center on Education Policy (CEP), an independent nonprofit organization, examines progress in raising achievement for English language learners. It also describes the factors that make it difficult to accurately assess what ELLs know and can do. The data for this analysis were collected by CEP with technical support from the Human Resources Research Organization (HumRRO) and come from the state reading and mathematics tests used for NCLB accountability in all 50 states. The trends discussed in this report cover fewer years--2006 through 2008--than the trends in recent CEP reports on achievement for students as a whole and achievement gaps for student subgroups. This is because revised federal regulations for testing ELLs and determining their progress under NCLB became final in September 2006. In general, English language learners have shown progress on state tests, but this positive news should be viewed somewhat cautiously because language barriers, demographic changes, and changes in state policies for testing and classifying students as ELLs make it difficult to obtain an accurate picture of achievement for this group. (Contains 7 footnotes and 5 tables.) [For the companion reports of this record, see the following: Part 1 (ED506121); Part 2 (ED506122); Part 3 (ED507909); Part 4 (ED509022); and Part 5 (ED509023).]