Chemistry concepts in three 2-week modules were presented to a treatment and control group of high school students from 10 different high schools. The treatment group was taught using three representations of matter (macroscopic, particulate, and symbolic), whereas only two representations (macroscopic and symbolic) were used with the control group. The treatment group scored significantly higher across the combined score of all three modules. When the data were analyzed for gender–group interactions, females who were taught the particulate representation scored as well as males whereas those who were not taught the particulate representation scored significantly lower than males. Teaching males the particulate representation did not significantly affect males' achievement. © 2002 Wiley Periodicals, Inc. J Res Sci Teach 39: 911–927, 2002