The effectiveness of a formal charge method to draw Lewis structures that was developed by Curnow was studied quantitatively by direct comparison of two groups of students: one of which was taught the new formal charge method and another that was taught a traditional method. Students' marks on a common assessment were found to improve by approximately 5% when taught the formal charge method, and students who used this method were able to identify the correct answer with fewer attempts. These differences were found to be statistically significant.