The average, honestly. Admission to Waterloo CS is based on an adjusted admission average (AAA): your top-six average, adjusted by AIF strength and contest performance. Published competitive averages sit in the mid-to-high 90s for the main CS program, but the AAA means two students with the same grades can land very differently depending on the rest of their file. Prerequisites are non-negotiable. You need Grade 12 Advanced Functions, Calculus and Vectors, and English, plus one additional 4U/4M course. Computer Science is not a required course for admission, but taking it helps you (and your AIF) — and doing well in Grade 11 CS keeps the door open for the stronger Grade 12 version. The AIF and interview. The AIF is required, and there's an optional AIF interview that Waterloo explicitly recommends for CS applicants. The interview is a conversation about your activities and interests — preparation matters more than charisma. Write the AIF as if it can move your average, because it can. Contests genuinely help. Waterloo runs the Canadian Computing Competition (CCC) and the Euclid contest, and strong results translate directly into a higher adjusted average. A top CCC Senior score is a genuine differentiator in a pool where almost everyone has a 95. Start practising years early — this is the one EC with a direct, quantified payoff.