This article considers the emerging method of design experimentation, and its developing use in educational research. It considers the extent to which design experiments are different from other, more established, methods and the extent to which elements of established methods can be adapted for use in conjunction with them. One major issue to be addressed before the metaphors and methods of design experiments can be fully accepted is that they assume the combination of different forms of data from different sources. How this combination takes place is, as yet, unresolved. The article, therefore, looks at similar problems also faced in 'new' political arithmetic, research syntheses and field trials to see how lessons learned in these approaches could help in the development of the design field.