Past counterfactual constructions of the type ‘If she had shut the cage, the rabbit wouldn’t have escaped’ form part of a wider set of conditional constructions expressing hypotheticality in English. Past counterfactual constructions were elicited from a large representative sample of UK 6- to 11-year-old children. They produced a total of 36 different ‘conditional-type’ constructions (as well as a number of non-conditional structures) in response to the task. Despite this variety, developmental trends were seen in the data as well as evidence of possible sociolinguistic variants on the standard English form given above. Moreover, children’s productions showed systematicity which revealed their tacit knowledge of the structure of conditional forms and their use. Wider implications, including children’s variable control of grammatical features thought to be earlier-acquired, and the possibility that adult usage is far more variable than is suggested by traditional hierarchies of conditional forms, are also discussed.