What i have been told is that these schools really emphasize two things on the academic side - academic reputation of your high school, and rigorous nature of the course of studies you followed. It is a given that you have top notch grades while taking those rigorous courses. The SATs; ACT scores cannot be dispensed with by any means, but their importance has been lessened within the last several years.
The poster who mentioned the A;B; and C variables is right on the money. One has to remember, however, these are some of the most competitive academic schools in the nation, and even the "C" acadmics are relatively strong.
That said - if you think your child is in the ballpark why not just speak with the coaches. They will provide a very realistic assessment of the situation. No loss in trying.