Science is always changing. Its very nature requires that scientists constantly revise theories to make sense of new observations. As they learn science, students are also constantly revising how they make sense of their observations, which requires comparisons with what they already know to process new information. A teacher can take advantage of this scientific way of thinking to shape instruction. By employing preassessments in the classroom, teachers can make a positive change toward further promoting meaningful learning for students. When building instruction on students' preconceptions, teachers can effectively reinforce, remediate, and develop new understandings. Chemistry is the science of change, and it begins with the knowledge that is shaped in physical science. Establishing an understanding of the particulate level changes students' view of the observable world and enables them to develop accurate scientific understanding that will benefit future learning. By using a preassessment of chemical and physical change, the teacher can become better equipped to bridge conceptual gaps through instruction. (Contains 3 figures.)