Through a literature review and an analysis of student files of the London (Ontario) Board of Education, researchers made several findings on the effects of school absence on students' academic achievement. The literature review first revealed four problems in interpreting research results, involving identification of the reasons for absence, measurement of the time absent, awareness of absence's complex effects, and consistency in attendance recordkeeping. The publications reviewed related absence to (1) student characteristics (sex, grade level, and attitude toward school); (2) family characteristics (socioeconomic status and parental attitudes); (3) school characteristics (academic quality and teacher attitudes); and (4) environmental variables (weather or day of the week). Files covering the entire elementary and secondary academic histories of 3,179 students who entered grade nine in 1965-66 were analyzed statistically. Student variables examined included sex, grade, mobility, intelligence, achievement, grade repetition, and non-London residence. Among the findings were that absence has a negative effect on achievement at the elementary as well as the secondary level; that the pattern of absence in elementary school affects absence in secondary school; and that the effect of absence varies with the student's intelligence. (RW)