This report reveals the problems with claims made by Arizona state public education officials that English Language Learners (ELLs) are thriving under English-only instruction. The No Child Left Behind Act of 2001 (NCLB) and the state's accountability system, Arizona LEARNS, require all students, including ELLs, to participate in statewide high-stakes testing. Test scores are the main measure of student achievement under these systems, and labels based on those scores are given to each school (i.e. Highly Performing, Underperforming, etc.). The state education administration's interpretation and strict enforcement of Proposition 203 has ensured that nearly all ELL students in grades K-3 are instructed through the English-only Sheltered English Immersion (SEI) model. They claim that SEI has led to better test scores and increased achievement among ELLs, using as evidence improved test scores and the decrease in the number of schools labeled as "Underperforming." However, analyses of test data for students in grades two through five and changes in the state accountability system revealed the contrary; they exposed serious achievement gaps between ELLs and their counterparts, and proved that positive looking improvements in school accountability labels mask test-score decline in a large number of elementary schools. (Contains 18 figures, 8 tables and 55 notes.)