To look at JLS, which was traditionally the ms feeder into Gunn (although that is changing) we only need to look at what is happening. The band and orchestra programs are growing so much that the concerts have to be separate to enable both programs enough time and space for parents at the concerts. Music is often the one extra curricula activity that academic minded parents allow because of all the studies that says musicians produce better academics.
On the other side, for example the 6th grade basketball program at JLS struggled to field three teams, some members of which had never played Y Ball or NJB and had perhaps done one summer camp in the sport, whereas Jordan had 6 or 7 teams. The calibre of these teams were also much higher than the JLS offering.
Another way of looking at this is Little League Baseball. This sport is run outside of schools, but does have a north/south divide on Oregon and Page Mill which is similar to the high school divide. The teams in the north are growing at an alarming rate and the increases are being made here. The teams in the south are not, and in fact there was discussion this season of reducing the number of majors teams because of lack of talented players at this level. The fact that the good south teams struggle to beat an average north team coupled with the fact that this weekend's tournament is between two north teams shows where the talent does lie.
It does appear that the families who are interested in doing well in academics move into the Gunn area, whereas those who want to do well in sport move to the Paly district. For an average sports player, it may be argued that they move to the Gunn district so that they have a better opportunity of getting onto one of the senior teams.
To say that the people who value academics are typically of one ethnic group and the sports from others, may lead to this post being edited, so we should not go there. But, the fact remains, this city is getting divided by the American love of sport!!