Can educational experiments both test a theory and inform practice?

This article feeds into debate about the feasibility and usefulness of educational experiments by discussing methodological issues arising out of a study which sought causal links between teaching and learning of one aspect of French as a foreign language. The study involved two small-scale experiments which tested a hypothesis regarding the learning of second language grammar within a particular theoretical, and its related pedagogical, framework (Input Processing and Processing Instruction respectively), and has been described in full elsewhere. The current article uses that example to suggest some circumstances (contextual, methodological and theoretical) within which educational experiments may be able to both test a learning theory and inform educational practice. It is argued that despite the complexities and limits of small-scale educational experiments, an experimental design which combined a range of methods was able to generate new and useful (in a range of senses) substantive knowledge.