This article reports an experimental study of the differential effects ofpremodified input, interactionally modified input, and modified output on the comprehension ofdirections in a listen-and-do task and the acquisition of new words embedded in the directions.The modified output group achieved higher comprehension and vocabulary acquisition scoresthan either of the input groups. There was no difference between the premodified andinteractionally modified input groups. The advantage of the modified output group is explainedin terms of the qualitatively superior dialogic interaction that occurred in this condition ratherthan in terms of actual language production.