This report summarizes information about student achievement, student opportunity to learn in science and mathematics, and student variables relating to that achievement for elementary and secondary students in the state of Illinois. Five tests were used for the basis of this report: The Illinois Inventory of Educational Progress, the American College Test (ACT), the Scholastic Aptitude Test (SAT), the High School and Beyond Test (HSB), and the Decade Study. The major findings indicate that (1) Illinois students' performance in high school science is essentially the same as the average performance nationally, (2) elementary school mathematics achievement in Illinois has risen significantly since 1976, (3) average mathematics scores for Illinois high school students are approximately the same as the national average on national tests, (4) state ACT scores in mathematics are lower than in 1972, (5) state SAT scores in mathematics remained stable throughout the 1970's, (6) Illinois high school level mathematics achievement is significantly lower that in 1970 on the Decade Study Test, (7) there are no significant differences between student performance in public and private high schools in the state on the ACT and HSB, and (8) male students score significantly higher than female students in mathematics and science in Illinois (the differences have decreased in mathematics and increased in natural science). (PN)