As part of an investigation of the effectiveness of a microcomputer-based laboratory (MBL) activity in developing students' graphing skills, this study was specifically designed to examine the differences between females and males in both performance on graphing tasks and on their attitudes to graphs and graph-based activities. Results based on a pretest of the participating secondary level students (N=93) revealed that about one-fifth of the students were seriously restricted in their ability to understand graphs by an inadequate graph schema. Females who had poor graph schemas appeared to have been constrained by their comparatively low ability, whereas the males were more likely to have been constrained by lack of interest. After controlling for differences in ability, some sex differences in performance on graphing tasks remained. Females had lower scores for items involving speed or velocity graphs, but not for graphs of miscellaneous graphs of less abstract properties such as distance. Discussed in this paper are two treatment groups that constructed distance and velocity graphs for one class period: (1) MBL group (N=18) used the microcomputer; (2) second (control) group (N=18) used paper and pencil. The females who participated in the MBL treatment gained significantly higher scores on a posttest of distance graphs, than the males did, while the reverse was true for velocity items. There were no sex differences for students in the control treatment. It was concluded that the MBL experience was effective in improving students' graphing skills. (ML)