Average differences in children's language abilities by socioeconomic status (SES) emerge early in development and predict academic achievement. Previous research has focused on coarse-grained outcome measures such as vocabulary size, but less is known about the extent to which SES differences exist in children's strategies for comprehension and learning. We measured children's (N = 98) comprehension of passive sentences to investigate whether SES differences are more pronounced in overall knowledge of the construction or in more specific abilities to process sentences during real-time interpretation. SES differences in comprehension emerged when syntactic revision of passives was necessary, and disappeared when the need to revise was removed. Further, syntactic revision but not knowledge of the passive best explained the association between SES and a standardized measure of syntactic development. These results demonstrate that SES differences in syntactic development may result from how children recruit syntactic information within sentences.