Ellis, Tanaka and Yamazaki (1994) compared people who could stop and work the meaning out in conversation with people given a simplified script and no talking back. The conversation group understood more, and they kept more of the new words.
Understanding is not the same as speaking. Immersion classrooms showed children who could follow a lesson still stumbled when they had to produce the language themselves. Swain and Lapkin (1995) is a good place to start if you want the idea of that stretch — output, or pushed speech — not a slogan.
Sources
Ellis, R., Tanaka, Y., & Yamazaki, A. (1994). Classroom interaction, comprehension, and the acquisition of L2 word meanings. Language Learning, 44(3), 449–491.
Swain, M., & Lapkin, S. (1995). Problems in output and the cognitive processes they generate: A step towards second language learning. Applied Linguistics, 16(3), 371–391.