Critical thinking is a systematic process in which information is manipulated to arrive at an answer or conclusion. This method can be divided into five different components: specific knowledge base, experience, competencies, attitudes and standards. We aim to assess these components of critical thinking within biology. We developed this assessment with the aim of distributing the instrument to Peer Leaders (PL) in order to evaluate the relationship between the time of exposure to the PLTL model and the critical thinking ability of the PL. We are working on establishing the assessment’s statistical validity and reliability methods. This research will help assess the differences in critical thinking skills between PLs and other biology undergraduate non-PLs to establish the effect the PLTL program has on students’ critical thinking ability.