This paper analyses Twitter microblogs over a 3-day period, during the release of the results of PISA 2015 on 6 December 2016 by the OECD. We document a methodological approach to investigating the social mediatisation of policy and its inclusive potential for enabling the participation of multiple voices. We draw on two data sets from the 3-day period: first, a large data corpus (n = 17,260) of all microblogs about PISA, and second, a smaller cluster of selected participant groups, notably academic, OECD, and teacher union actors (n = 65). Our analytic tools provide a methodological heuristic for scoping social media networks. Our research is guided by questions about 'Who participates?' in PISA debates and 'What is being said?' and considers the volume, engagement, and content of the microblogs. Of the three participant groups, the academic actors authored the largest volume of microblogs across the corpus and cluster. The content of microblogs from the OECD cluster mainly provided information about and promotion of PISA, while the academic cluster emphasised commentary and critique, with all actors using an analytic tone. The OECD had the largest number of followers and the highest rate of social recommendations and engagement with their microblogs.