Play is a core resource for how children learn. Yet current efforts to bring playful learning into schools often neglect the role adults play in embracing and modeling playfulness. This paper presents findings from a collaboration between the International School of Billund, Denmark, and Project Zero, a research organization at Harvard Graduate School of Education. The study examined Playful Participatory Research (PPR), an emergent qualitative methodology that is both teacher research and a professional development (PD) approach. Drawing on interviews with 21 teachers across the school, we found that PPR positively affects: attitudes towards PD; teachers’ self-perception and identity; incorporation of play into teaching; and overall school culture. Implications suggest that school leaders who aspire to support learning through play in schools should design adult learning environments that mirror the playful learning environments they desire for children, by providing time, resources, and encouragement for playful teacher research and PD.