A topic of continued discussion has been whether international teaching assistant (ITA) education is best done within academic departments, or within university-wide programs organized by English as a Second Language (ESL) specialists. This report describes a pilot ITA practicum which may potentially combine the best of both approaches: Academic departments which seek to help ITAs learn how to teach within their disciplines, and a university-wide ESL program which is committed to developing ITAs' classroom communication skills. Through a cooperative effort, an ESL specialist and five academic departments paired 15 pre-service ITAs with experienced TA or ITA mentors, with the intention that over an entire semester, the ITAs would attend the mentors' classes, observe and listen to them teaching, and interact with and teach students. Using a student- and response-based evaluation approach, the report investigated the extent to which ITAs' participation in the practica generated significant opportunities for ITAs' second language acquisition in discipline-specific settings. Data from ITAs and mentors suggested that participants found the practica to be worthwhile and that ITAs had some opportunities to attend to input, interact with US undergraduates, and engage in comprehensible output. However, observations of ITAs in two departments revealed that opportunities for second language development varied depending on the format of the classes (lab versus lecture), and on personal attributes of ITAs. Although the study is limited, the results suggest the need for continuing the practica with revisions, as well as an overall need to conduct investigations into ITA second language acquisition as constrained by sociocultural contexts and ITA choices.