Gender differences in achievement were studied in five academic areas: (1) vocabulary; (2) language usage; (3) reading; (4) mathematics problem solving; and (5) using sources of information. Standardized achievement test scores for a sample of 3,002 students (1,642 females and 1,360 males) who were tested in each of 10 consecutive years, grades 3 through 12, were used to assess these differences. Data were from the Iowa Statewide Testing Program, using the Iowa Tests of Basic Skills and the Iowa Tests of Educational Development. Selected percentiles used to estimate both female and male score distributions for each subtest area were: 90th; 75th; 50th; 25th; and 10th. Results show fairly consistent patterns of differences. Males generally performed better at the upper percentile levels in vocabulary and mathematics problem solving, and females performed better at lower percentile levels in all content areas, as well as at all percentile levels of the score distribution and across all grades for the language usage area. Developmental patterns of differences between male and female performance appeared when different ability levels were examined. Seven tables and five graphs present study data. (SLD)