Two-year-olds learn language quickly but how they exploit adult input remains obscure. Twenty-nine children aged 2;6 to 3;2, divided into three treatment groups, participated in an intervention experiment consisting of four sessions 1 week apart. Pre- and post-intervention sessions were identical for all children: children heard a wh-question and attempted to repeat it; a 'talking bear ' answered. That same format was used for the two intervention sessions for children in a quasicontrol condition (Group QC). Children receiving modelling (Group M) heard a question twice before repeating it; those receiving implicit correction (Group IC) heard a question, attempted to repeat it, and heard it again. All groups improved in supplying and inverting an auxiliary for target questions with trained auxiliaries. Only experimental children generalized to auxiliaries on which they had not been trained. Very little input, if concentrated but varied, and presented so that the child attends to it and attempts to parse it, is sufficient for the rapid extraction and generalization of syntactic regularities. Children can learn even more efficiently than has been thought.