This paper deals with the history and practices of the language assessment policy being used by the state of Illinois' transitional bilingual education programs serving over 42,000 students. The first section of the paper treats the history of bilingual program evaluation efforts. It divides the discussion into three periods, prior to 1976, from 1976 to 1979, and current activities and special projects. Part two deals with Illinois' uniform data collection procedures, which provide the framework for the longitudinal studies that began with the first annual "Program Summary and Evaluation Report" in 1980. The components of these procedures are the public school bilingual census, program application, student cumulative record, and the annual student report. The final section of the paper outlines the information that was obtained as a result of the data collection and language assessment policy. These findings derived from questions related to issues such as transition and exit rates, program participation information and student identification information, and analysis of achievement as a measure of program exit. A discussion of several language proficiency testing instruments completes the paper. (Author/AMH)