Uruguay did not have enough data to be listed, but the years I took the Cambridge and Oxford language tests (FCE, Proficiency, etc.), Uruguayans were in the top spots (the #1 overall got a scholarship to Oxford, and she was Uruguayan).

Of course, the demographics very much the same as Argentina's so it wouldn't be a big difference (we're not an Argentinian province by political accident and meddling by Britain - not that we mind :) ).