The NRC from each education system was responsible for data entry. In the United States, RTI International was contracted to collect data for PIRLS 2016 and entered the data into data files with a common international format. This format was specified in the PIRLS Data Entry Manager Manual (IEA Data Processing Center 2015), which accompanied the IEA-supplied data-entry software (WinDEM) given to all participating countries to create data files. This software facilitated the checking and correction of data by providing various data consistency checks. The data were then sent to the IEA Data Processing Center (DPC) in Hamburg, Germany, for cleaning. The DPC checked that the international data structure was followed; checked the identification system within and between files; corrected single case problems manually; and applied standard cleaning procedures to questionnaire files. Results of the data cleaning process were documented by the DPC. This documentation was then sent to the NRC along with any remaining questions about the data. The NRC then provided the DPC with revisions to coding or solutions for anomalies. The DPC subsequently compiled background univariate statistics and preliminary test scores based on classical item analysis and item response theory (IRT). Detailed information on the entire data entry and cleaning process can be found in the Methods and Procedures in PIRLS 2016 (Martin, Mullis, and Hopper 2017), available at https://timssandpirls.bc.edu/publications/pirls/2016-methods.html.