The US Government Accountability Office (GAO) began a study to compare English Language Learner (ELL) enrollment in charter schools to ELL enrollment in traditional public schools. For the study, they obtained ELL enrollment counts for school year 2010-11 from the U.S. Department of Education's (Education's) only available dataset containing the necessary school-level data. In accordance with Government Auditing Standards and GAO policy, they assessed the quality of the ELL data as part of the study and found problems with the data's quality that prevented them from completing the study. This letter addresses: (1) the quality of Education's data on ELLs in charter schools; and (2) the efforts taken by Education to improve its collection of ELL data from charter schools. This review was conducted from November 2012 to July 2013 in accordance with generally accepted government auditing standards. Based on the findings of the review, GAO recommends that Education systemically evaluate the extent of charter school nonreporting across other data sets and explore whether collection of the poorly defined ELL data can be phased out at the local educational agency (LEA) and state levels, if the data quality problems are not addressed.