<p>My observation is that the "ED advantage" is much more evident at LACs than it is at super-selective universities. I don't see SCEA making a whole lot of difference to admissions at Yale or Harvard, but I do see ED being a significant advantage at Williams/Swarthmore/Amherst. </p>
<p>Yield is one reason and fit is another. These schools have very small classes and everyone needs to work and play well together as well as contribute to more than one aspect of campus culture, so if a student fits, is multi-faceted and is guaranteed to attend then s/he becomes a person of interest -- as long as s/he is academically qualified.</p>
<p>Academically there is no borderline at these schools (just very good and excellent), but they do evaluate an amalgam of statistics (GPA, rank, scores) and less objective factors such as essays, recommendations, talents and demographic contributions and one area of strength can counterbalance a relative weakness.</p>
<p>Another point to consider is that the applicant has absolutely no control over his/her competition. In the ED pool there are fewer applicants and less chance of direct overlap. Plus the highest academic achievers are not likely to be in the AWS ED pool as they are more likely to want to apply to HYPSM as well and make their decisions in April.</p>
<p>The OP's son for example is a football playing musician with an interest in law. Not the only one, certainly, with an interest in Swarthmore but among their ED pool, I would think one of few. [And here I can't resist asking, why not Williams?]</p>
<p>Case in point: No one from my son's high school had gone to Williams for years. The counselors weren't particularly interested in or enthusiastic about the school and it didn't appear on too many lists. My son, as noted, applied and was accepted ED. What we found out later was that his highschool Sal, also applied to Williams in the RD round. Now this kid is a superstar -- perfect grades and scores, dual nationality, several languages, two varsity sports, all around nice guy, AND he plays the trombone. He was accepted at every school he applied to including the most selective ivies. He chose Williams. </p>
<p>This highschool is a very small, international school. Even though these two candidates had very different profiles it's doubtful that Williams would have accepted both, so in my son's case I think there was a hidden advantage to applying ED.</p>