Based on current theories of chemistry learning, this study intends to test a hypothesis that computer modeling enhanced hands-on chemistry laboratories are more effective than hands-on laboratories or computer modeling laboratories alone in facilitating high school students' understanding of chemistry concepts. Thirty-three high school chemistry students from a private all-girl high school in northeastern United States were divided into two groups to participate in a quasi-experimental study. Each group completed a particular sequence of computer modeling and hands-on laboratories plus pre-test and post-tests of conceptual understanding of gas laws. Each group also completed a survey of conceptions of scientific models. Non-parametric tests, i.e. Friedman's one-way analysis of ranks and Wilcoxon's signed ranks test, showed that the combined computer modeling and hands-on laboratories were more effective than either computer simulations or hands-on laboratory alone in promoting students' conceptual understanding of the gas law on the relationship between temperature and pressure. It was also found that student conception of scientific models as replicas is statistically significantly correlated with students' conceptual understanding of the particulate model of gases. The findings mentioned earlier support the recent call for model-based science teaching and learning in chemistry.