This paper presents primary teachers’ and university-based teacher educators’ experiences of integrating language and content when teaching physical education (PE) through Irish. Two teacher educators, a language specialist and a content specialist collaborated in professional development (PD) with primary teachers in English-medium (n = 2) and Irish-medium immersion schools (n = 2) to teach two units of PE. A design-based research methodology was adopted in two six-week cycles. Qualitative data were collected from: individual interviews and a focus group interview with teachers, teacher educators’ reflective diaries and observation of PE lessons. Successes of the approach were children’s enjoyment and language development supported by the pre-teaching of language. Balancing language and content was found to be challenging for teachers in both linguistic contexts. This study suggests that dual-focused collaborative PD and tailor-made resources are necessary to support generalist teachers in navigating the complexity of integrating language and content in CLIL and immersion contexts.