Development of the control of variables strategy in physics among secondary school students

This study explores the developmental trend in scientific reasoning in the control of variables strategy (CVS) and how relevant factors contribute to explaining the individual abilities of secondary school students. A cross-sectional investigation involving 807 students from Grades 8 to 12 was conducted in eleven public schools in Vietnam. A 24-item test assessed CVS in basic physics (mechanics, thermodynamics, and electricity), emphasizing three CVS subskills (identifying controlled experiments, interpreting controlled experiment outcomes, and understanding the determinacy of confounded experiments). The results showed that the students’ CVS capacity increased in a nonlinear pattern across grade levels with a model fitting in the symmetric logistic function, in which the most rapid growth was flagged in the second year of high school. Although there was no significant difference for gender in CVS either within each grade cohort or within the whole sample, the mean score favoured males on the item bundle of understanding the determinacy of confounded experiments. Furthermore, multi-model Bayesian inference suggested that grade level (or student age), prior content knowledge, and mother's education were better factors in predicting students’ CVS capacities in this study. The implications for implementing the findings in educational practice are also discussed.