The long-standing challenges and issues associated with girls' disengagement from secondary school physical and health education (PHE) are serious and well documented. This disengagement has provided the incentive for the examination of alternative strategies to facilitate girls' engagement in PHE. This paper discusses the first phase in a formative research process designed to develop a resource manual to help teachers utilize nature-based physical activity (NBPA) as a means of fostering relatedness for girls in PHE. Participating teachers collaborated and generated specific NBPA ideas and pedagogical strategies during an all-day planning session. Four focus groups with the teachers (N = 20) were used to identify ways to develop NBPA interventions. Five broad topics are reported: (a) defining NBPAs, (b) specific NBPAs to use in PHE, (b) how NBPA can foster relatedness, (d) how NBPA in PHE differs from outdoor education, and (e) barriers to implementing NBPA in PHE. This paper emphasizes the valuable contribution of formative research to the integrity and fidelity of an intervention as well as to quality practice in the implementation of theory-based PHE initiatives.