Teachers’ informal professional development on social media and social network sites: when and what do they discuss? Jorryt van Bommel 1 & Yvonne Liljekvist 1,2 1 Karlstad University, Sweden jorryt.vanbommel@kau.se 2 Uppsala University, Sweden Abstract: In recent years, a digitally extended context for teachers’ professional learning has arisen. Digital gadgets (smart phones, etc.) alongside the development of social media and social network sites change how people interact and work together, and, hence, teachers initiate and orchestrate their own professional development on the Internet. In this paper we report on an on-going three-year study and show some of the prospects of conducting research on mathematics teachers’ informal professional development on social media and social network sites, and, furthermore, discuss the need for theoretical and methodological development. Keywords: Teachers’ professional development, Social media, Facebook, digital. INTRODUCTION In communities where digital gadgets (e.g., smart phones, applets, laptops, etc.) are in common use, people change how they work, interact and communicate. The arena for professional development has accordingly transformed and branched out into the Internet. In the literature we now find studies examining social media and social network sites as a means for teachers’ professional learning and knowledge-sharing (e.g., Al-Oqily, Alkhatib, Al-Khasawneh, & Alian, 2013; Bissessar, 2014; Borba & Llinares, 2012; Hew & Hara, 2007; Liljekvist, 2014; Manca & Ranieri, 2014; Pepin, Gueudet & Trouche, 2013; Rutherford, 2010; van Bommel & Liljekvist, 2015). The findings show that teachers use different forums on the Internet, such as, Twitter, Web sites, personal blogs, and Facebook, as resources to share and develop pedagogical subject-matter knowledge, to ask for and give pedagogical advice, etcetera. Thus, the arena for professional development of teachers has changed. Teachers not only engage in traditional forms of professional development activities, such as, taking courses, reading books, and participating in the local school colloquium. They also engage in new forms of professional development made possible by the evolution of the Internet. Online courses, web-seminars and other formal professional development are widely spread nationally as well as internationally. Another trend is also evident: Teachers initiate and orchestrate their own professional development on the Internet. This phenomenon promotes reflection upon social