Dynamic assessment (DA) integrates assessment and instruction into an organic unity aimed at promoting learner development through mediation sensitive to the individual's (or in some cases, a group's) current abilities. This article reports on the construction of a model of mediation framed within DA for English-as-a-foreign-language listening comprehension. The model was implemented in a 1-semester comparative experimental study in 2 parallel classes of Grade 8 in an urban middle school in central China. For mediation, the experimental class (EC) received four DA sessions aligned to their emerging abilities at all listening stages. Statistical results showed that students in EC outperformed those in the control class significantly in both a posttest and a near transfer assessment test, a more complex task intended to assess development in a more accurate manner, although they showed no significant advantage in the far TA test. Microgenetic analysis of the development of a sample of 9 students revealed that the mode of mediation used during enrichment permitted the teacher to ascertain students' listening problems, including their struggles with phonology, lexicon, grammar, and strategy use. The value of the DA mediation model is discussed as a dialectical unity of both a diagnostic tool and a pedagogical framework in the context of young L2 learners.