Background: There are approximately 52,000 teacher-coaches coaching 750,000 high school student-athletes in Canada. Despite this large population, Canadian high school teacher-coaches remain relatively unstudied. High school coaches in Canada are often asked to coach sports with which they are unfamiliar, and because they are not required to obtain formal training, they acquire knowledge from various situations in order to meet their learning needs. Purpose: The purpose of this study was to understand how high school teacher-coaches learn to coach, using Jarvis' theory of human learning. Participants and setting: Thirty-one high school teacher-coaches (15 females and 16 males) from 17 schools (12 urban and 5 rural) in Ontario, Canada, participated in this study. All the participants had a minimum of one season of experience as the head coach of a high school sport team. Any sport offered by the Ontario Federation of School Athletic Associations at any level (midget, junior, or senior) was an acceptable fulfilment of this requirement. Data collection: The participants were interviewed in person at mutually convenient time and location. Interviews ranged from 30 to 75 minutes. Two focus groups, with three participants each, were conducted in two separate schools. Focus groups were conducted during lunch or after school hours at the participants' school. Data analysis: Interviews and focus groups were transcribed verbatim amassing 464 single-spaced pages of data. A theoretically driven thematic analysis was conducted and the data were coded under three main headings: formal, non-formal, and informal learning situations, and further coded using concepts from Jarvis' theory of human learning. All of the coded data were re-read and sorted into potential themes and relationships between themes and codes were identified. Findings: Results indicated that a large number of teacher-coaches had formal coach training, despite it not being mandatory. However, their appreciation of this learning situation was tempered by their biographies. Coaching clinics were viewed as an occasion to develop sport-specific competencies, especially when coaching a sport in which coaches had limited knowledge. Informal learning situations, such as past coaching and/or playing experience, were two life experiences regarded as useful for learning to coach. Interaction with colleagues was utilised by all the participants as a means of developing coaching knowledge. Lack of time was a major factor influencing the type of situations from which teacher-coaches chose to learn. Conclusions: Tailoring coach learning resources to teacher-coaches' needs and schedules would help improve their coaching competencies and ultimately maximise the benefits of high school sport for all involved.