Proof validation plays a significant role in students' understanding and learning of mathematical proofs. Recent studies have shown that university students were lacking skills in proof validation and were challenged by the implementation of the appropriate acceptance criteria when validating proofs. Drawing on Habermas' construct and rational questioning, the present study develops a proof validation framework that seeks to improve students' proof validation skills. The written responses of students' proof validation were analyzed based on their use of the proof validation framework in the context of a transition-to-proof course. The results showed that students primarily focused on the epistemic rationality component when they accept or reject the purported proof and that the students experienced difficulties with meeting the requirements of rationality components. Some educational implications are provided. [For the complete proceedings, see ED657822.]