This report on student achievement in Illinois describes and synthesizes the results of six different measures of the achievement of Illinois students. The six tests are: (1) Illinois Inventory of Educational Progress, (2) Decade Study Test, (3) High School and Beyond Test, (4) Scholastic Aptitude Test, (5) American College Test, and (6) National Assessment of Educational Progress. These instruments are described in tabular form in terms of the students tested, curricular areas assessed, and overall purpose. This report provides an analysis of student progress across years, from basic to advanced skills in reading, language arts, social studies, mathematics, and science. An attempt has been made to integrate the results of the six measures of achievement to obtain a more complete picture of the performance of Illinois students and, indirectly, Illinois schools. This study of student achievement was conducted to answer three major questions: how well are Illinois students performing in academic areas as compared to students in other parts of the nation and the nation as a whole?; how well are Illinois students of today performing in academic areas as compared to Illinois students during the last decade?; and what student and school characteristics are related to achievement of Illinois students? (PN)