Studies of statistical learning have documented a remarkable sensitivity to structural regularities in both infants and adults. However, most studies of statistical learning have assumed a single underlying causal structure with uniform variance. In previous work in which two structures are presented successively, a primacy effect has been reported in which only the first structure is acquired. The present study explores the conditions under which such primacy effects are observed and learners are capable of acquiring both structures. We argue that learners can detect multiple structures by monitoring the consistency of the input.