Critical care nurses need to possess theoretical knowledge, advanced skills as well as competencies and capabilities to care for critically ill patients in the challenging and fast changing environment of intensive care. In order to assess performance and learning in critical care nursing students in the clinical setting, a structured process enabling college faculty, clinical educators and students to work towards the same goals and learning outcomes is of outmost importance. In this study action research was used to develop an assessment instrument in a collaborative effort between faculty, clinical educators and students. The instrument was developed and tested at several clinical sites during a period of 11/2 years. Interviews were conducted with expert focus groups and students about the ease and feasibility of the instrument. Four themes emerged during the analysis of the interviews: clarity,helping me, arranging and timeliness. The analysis further revealed positive opinions about the structure, content and usability of the instrument. We conclude that the instrument helps in both assessing student performance and in revealing knowledge-gaps for the students in the critical care nursing program.