Educators must consider how today's technology-mediated environments expand our conceptualization of learning contexts and the continuities and tensions between learning and participation in various settings. The COVID-19 pandemic disrupted educational systems worldwide, necessitating emergency remote teaching and coinciding with increased social media use. Such shifts require reconceptualization of learning boundaries in a digital age. This article explores British and American teachers' professional learning spanning social media, place and time. We collected #UKEdchat tweets and #Edchat tweets over 28 months, 1 January 2019-30 April 2021, and identified tweeters who were middle or secondary school teachers in the U.K. and U.S. to interview. From analysis of these data, we report on the tensions, synergies and experiences of boundary-crossing teachers with implications for research and practice.