In fiscal year 2007, Arizona’s 138,449 English Language Learner (ELL) students composed approximately 14 percent of the total student enrollment compared to the national percentage of 10 percent. Beginning in fiscal year 2009, these students must be taught using State-developed Structured English Immersion (SEI) models incorporating 4 daily hours of English language development (ELD). This special study found that the current programs at a sample of Arizona school districts and charter schools will need to make significant changes to comply with the new SEI models. For example, only 3 of the 18 programs sampled were operating classes that met the 4 hour ELD requirement, and these classes were not offered to all ELL students. The study also found that basic data about the number of ELL students, their English proficiency, and their time in the ELL programs was often lacking or inaccurate. For example, some students were enrolled in the programs despite assessment scores rating them as English proficient, while other students were reclassified as proficient although their assessment scores still showed them to be below proficient. The Arizona Department of Education must ensure that there is sufficient, accurate data to manage, fund, and conduct future evaluations of the success of the program.