Many undergraduate students have difficulty writing mathematical proofs even though this skill is important for the development of future teachers and those who may be involved in instruction or training as a graduate student or supervisor. In addition, research indicates that mathematics majors and secondary education mathematics majors possess little ability to determine whether arguments are valid proofs. Asking students to validate proofs using specific activities may not only help undergraduates develop the ability to validate proofs, but also may help increase their own proof writing abilities. The purpose of this study was to investigate the effect of proof validation on the ability to write proofs. Two sections of abstract algebra were the focus of a "guided research" study--one section was taught using a weekly proof validation activity and the other was taught as a control group. Data analysis revealed that the validation group significantly outscored the control group on items involving proof writing on the final exam. Results of the proof validation activities are also presented. (Contains 1 table.)