This study involved the evaluation of the efficacy of a planned instructional program to facilitate understanding of the macroscopic, submicroscopic and symbolic representational systems when describing and explaining chemical reactions by sixty-five Grade 9 students in a Singapore secondary school. A two-tier multiple-choice diagnostic instrument consisting of fifteen items was administered after nine months of instruction. Analysis of the students' performance on the diagnostic test, showed improved understanding of the use of multiple representations compared to that of seventy-six students of similar achieving ability in the prescribed program of instruction. (Contains 1 table and 3 figures.)