In this study, we explore the following: a) How do secondary student teachers, engaged in collaborative action research, function as critical friends? b) What challenges do they encounter? How do they mitigate these challenges? and c) In what ways did meeting as critical friends influence the student teachers' learning to conduct collaborative action research? The participants in our study included 38 secondary school student teachers (defined here at grades 9 through 12) in the last year of a two-year Masters program from a large, research-intensive university situated in the West of Ireland. The student teachers were organized into 11 critical friend groups of three to five members focused on conducting collaborative action research on the integration of different approaches to lesson planning. Four university supervisors guided the critical friend groups on the topic of lesson planning and offered three lesson plan templates including a long form, shortened form, and a form created by the student teachers themselves. Data were gathered via group feedback forms, surveys, and action research papers. Data analysis entailed the use of open coding, categorization of recurring codes, and analytic memos. Assertions were generated based on recurring trends in the data. Findings indicated that student teachers as researchers have the capacity to leverage the resources, skills, and knowledge gleaned from their critical friend groups to advance their development as teachers and teacher researchers. Their collaborative relationships help ensure a sense of confidence and respect for one another and for the teaching profession itself.