The research presented in this paper consisted of an investigation of the effectiveness of a four-step constructivist-based teaching activity on student understanding of how pressure and temperature influence the dissolution of a gas in a liquid. Some 44 Grade 9 students (18 boys and 26 girls) selected purposively from two school classes in the city of Trabzon, Turkey participated in the study. Students' understanding were evaluated from examination of two items from a purpose-designed solution concept test, face-to-face semi-structured interviews and examination of students' self-assessment exercises. Statistical analysis using two-way ANOVA of student test scores point to statistically-significant differences in test and total scores (p less than 0.05) suggesting that the teaching activities employed help students achieve better conceptual understanding. Further, no statistically significant differences were seen between post-test and delayed test scores, suggesting that teaching the activities enable students to retain their new conceptions in their long-term memory. However, in a few instances the activities resulted in the development of new alternative conceptions, suggesting teachers need to be conscious of the positive and negative effects of any teaching intervention.