This research study employed a mixed methods approach to explore connections between teachers’ use of online technologies in their personal lives, for professional development and/ or within classroom practice in Ireland and the USA. In phase 1 of this study, over 80 Irish primary school teachers’ experiences of online Continuing Professional Development (CPD) were examined, through the deployment of interviews, focus groups and an online survey. Almost half of the Irish teachers felt that engagement in online CPD impacted positively on classroom practice, and reported having integrated information and communication technologies in their teaching as a direct result of engagement in the online course. Phase 2 of the study examined online technologies usage in the personal lives, professional development and classroom practice of K-12 educators in the USA, through the deployment of an online survey (with 632 respondents) and follow-up interviews. The results revealed low levels of integration of social media in classroom practice, although there were strong correlations between US teachers’ use of online technologies and/ or social media in their personal lives, for professional development and within classroom practice. Recommendations that emerged from this study include the need for policies to support (rather than restrict) the use of social media in schools and the need for teacher training on how to effectively infuse online technologies and/ or social media in teaching and learning.