Some recent studies have suggested a significant bottom-up or parental component to recent movements for autochthonous minority language-medium education (MLME). This study takes MLME as the outcome of interest and seeks to explain trends in Irish-medium education (IME) in the Republic of Ireland and Northern Ireland since 1920--a unique opportunity for double comparison over space and time--as an example of MLME. A comparison of data from government statistical reports in the Republic of Ireland, and from government publications and previous studies in Northern Ireland, shows markedly different trends in IME before 1970 but convergence in patterns since. Theoretical analyses suggest that theories focusing on the individual are more valid for explaining trends from the 1970s, while those focusing on the collective have more explanatory power regarding trends from the 1920s to the 1970s. This supports the idea that the initiative for heritage language instruction has shifted from the state and other "official" agents to grass-roots agents such as parents. At the same time, it raises the question of whether the new positive trend in IME is lasting, or just a fad that can be easily exchanged for a new marker of distinction by aspiring social groups.