Would not say Summit, Manasquan, RFH, and Westfield do a great job of keeping kids public compared to Mountain Lakes. If you look at the rosters of schools like Delbarton, SHP, Pingry, Lawrenceville, and even NE prep schools, they are littered with kids from Summit every year. Same applies to Westfield for SHP, St. Peters, and Pingry. Less so with Delbarton and the prep schools. With regard to Squan and RFH, take a look at the rosters at CBA, Red Bank Catholic, Lawrenceville, Hun, etc. Ridgewood, Northern Highlands, and Ramapo are all in the same boat with loads of kids heading to the Bergen County catholic schools.
In Mountain Lakes, it is very very rare to see kids go to private school. Not sure how Flynn has done it but a Mountain Lakes resident going to Delbarton (really the only private school that makes sense geographically/athletically/demographically). | 
