This study of Chicago teachers' assignments in mathematics and writing in grades 3, 6, and 8 shows that students who received assignments requiring more challenging intellectual work also achieved greater than average gains on the Iowa Tests of Basic Skills in reading and mathematics, and demonstrated higher performance in reading, mathematics, and writing on the Illinois Goals Assessment Program. Data were from assignments collected in 1997, 1998, and 1999 with these sample sizes: (1) grade 3 writing, all 3 years, 1,785 assignments; (2) grade 6 writing, all 3 years, 1,686 assignments; (3) grade 8 writing, all 3 years, 1,425 assignments; (4) grade 3 mathematics, all 3 years, 1,794 assignments; (5) grade 6 mathematics, all 3 years, 1,522 assignments; and (6) grade 8 mathematics, all 3 years, 1,278 assignments. Assignments were scored by teams of teachers and scores were equated across years. Contrary to some expectations, the study found some high quality assignments in some very disadvantaged Chicago classrooms. It was evident that all students in these classes benefited from exposure to such instruction. Results suggest that if teachers, administrators, policymakers, and the public at large place more emphasis on authentic intellectual work in classrooms, yearly gains on standardized tests in Chicago could surpass national norms. Four appendixes contain details on study methodology. (Contains 5 figures, 24 endnotes, and 39 references.) (SLD)