The effect of a student-centered learning environment and a teacher-centered one on the understanding by middle school students of the topic of solid pressure has been investigated. A quasi-experimental research design with a control group was used. The participants in the study were students from a public middle school in Turkey. Before and after the formal teaching, students in the control and experimental groups were given the questionnaire that included open-ended questions related to the solid pressure topic. A rubric was used to analyse students' responses to open-ended questions. In the control group, the teacher based the activities on the textbook. In the experimental group, additional activities took place and a model related to the topic was used by the students. There is an increase in scientifically correct answers in both groups after instruction - larger in the experimental group. The decrease in misunderstandings was also larger in the experimental group. These results reveal that the uses of models and hands-on activities by students in the learning process have contributed more to understanding the solid pressure. Therefore, it is suggested to use such hands-on activities and models and to provide a learning environment for the students to practice them and thus to enhance their understanding of science.