The study described in this chapter examines whether practice with idioms can promote the acquisition of grammatical features of the language. Following the criteria for incidental learning described in Shintani and Ellis (2010), we designed a series of lessons based on Spanish idioms containing the copular verbs ser and estar (e.g., estar hasta el gorro ‘to be fed up’; ser pan comido ‘to be very easy’). Learners engaged in receptive practice activities that required them to demonstrate comprehension of the idioms. The participants (n=83) were assigned to one of two treatment conditions: 1) an incidental learning condition in which they were instructed on the meanings of the idioms and their appropriate use and 2) an enhanced incidental learning condition in which the same activities were implemented, but learners were directed to notice the copular verbs. The results provide some evidence of incidental learning, although the gains are most salient in one particular linguistic context: the use of estar for location. Differences between the groups are minimal and a post-study survey indicates that both groups reported similar levels of noticing the grammatical target of instruction. These results are discussed in relation to the findings of previous studies of incidental learning.