Research in mathematics education constantly oscillates between theoretical or 'Is' questions and practical or 'Ought' questions: Researchers are not only pursuing theoretical questions by investigating what those involved in the teaching and learning of mathematics do, but they are also working on practical recommendations for what they ought to be doing. And while research methods that underlie theoretical research have long been the subject of methodological discussion, the question of whether and, if so, how practical research in mathematics education is possible as a scientific endeavour has only recently become more central to the methodological debate. It is therefore this second question concerning the possibility of practical research in mathematics education which I will address in this paper.