Effects of microcomputer-based laboratories and level of cognitive development on tenth-grade biology students' ability to construct and interpret line graphs was investigated. Fortysix students enrolled in general biology classes at a rural high school volunteered to participate in the study. These students were administered instruments to assess level of cognitive development and line-graphing ability. Ten students that scored between zero and three and ten students that scored between six and ten on the graphing assessment were chosen to participate in the study. The 20 students were then assigned to either experimental or conventional groups to achieve a matched design with relation to gender and line-graphing ability. Statistical analysis of the data indicated no effect due to instructional method on graph-interpretation abilities. An instructional effect was demonstrated for graph-construction tasks (p < 0.10) with the conventional group outperforming the microcomputer-based laboratory group. Effect sizes of −1.01 and 0.48 were found for graph-construction and -interpretation skills, respectively. Effects related to cognitive development were indicated with those students classified as high cognitive development outscoring those classified as low (p < 0.10) This was true for both graph-construction and graph-interpretation tasks. No two-way interactions were found.