The Dalton Plan is well known in educational historiography. But there are also unanswered questions such as: how is it possible that a pedagogical experiment begun in the United States in February 1920 had, by the month of March, already come to be known first hand by a visiting English educator? The objective in this article is to find an explanation for the rapid expansion and huge popularity of the Dalton Plan in Great Britain in the early 1920s. This is attempted theoretically by using the concepts 'educational network' and 'pedagogical product', and empirically by using unexplored documents and correspondence concerning Helen Parkhurst's trips to Great Britain. It ends with the conclusion that, in Great Britain, as early as 1922, the Dalton Plan became a commercial product that was exploited in similar ways to the work of Maria Montessori.