Objective: develop and test a tool designed for use by preceptors/mentors to assess undergraduate midwifery students׳ critical thinking in practice.

Design: a descriptive cohort design was used.

Setting: participants worked in a range of maternity settings in Queensland, Australia.

Participants: 106 midwifery clinicians who had acted in the role of preceptor for undergraduate midwifery students.

Methods: this study followed a staged model for tool development recommended by DeVellis (2012). This included generation of items, content validity testing through mapping of draft items to critical thinking concepts and expert review, administration of items to a convenience sample of preceptors, and psychometric testing. A 24 item tool titled the XXXX Assessment of Critical Thinking in Midwifery (CACTiM) was completed by registered midwives in relation to students they had recently preceptored in the clinical environment.

Findings: ratings by experts revealed a content validity index score of 0.97, representing good content validity. An evaluation of construct validity through factor analysis generated three factors: ‘partnership in practice’, ‘reflection on practice’ and ‘practice improvements’. The scale demonstrated good internal reliability with a Cronbach alpha coefficient of 0.97. The mean total score for the CACTiM scale was 116.77 (SD=16.68) with a range of 60–144. Total and subscale scores correlated significantly.

Conclusion: the CACTiM (Preceptor/Mentor version) was found to be a valid and reliable tool for use by preceptors to assess critical thinking in undergraduate midwifery students.

Implications for practice: given the importance of critical thinking skills for midwifery practice, mapping and assessing critical thinking development in students׳ practice across an undergraduate programme is vital. The CACTiM (Preceptor/Mentor version) has utility for clinical education, research and practice. The tool can inform and guide preceptors׳ assessment of students׳ critical thinking in practice. The availability of a reliable and valid tool can be used to research the development of critical thinking in practice.