Students’ understanding of science has always been of considerable importance in the area of science education research at school level. It tries to focus on issues such as tools to aid understanding, conceptual understanding, tools for evaluating understanding, individual knowledge structure of students so on and so forth. Cognitive map is one such tool that is used to elicit understanding the subject thoroughly as well evaluating knowledge and teaching- learning process success in a given domain. Cognitive maps are two- dimensional hierarchical and node-like diagrams that depict knowledge. This paper presents a view of using cognitive mapping as tool for enhancing students’ knowledge structure and understanding and learning process in science. This study used two different methods of evaluation- achievement test and cognitive map test- for evaluating students understanding.  The study depicts the in the understanding and representation of concepts and propositions using cognitive maps as evaluation tool as compared to achievement test.