Prestige is context sensitive. Nature is the most prestigious scientific journal, but outside the scientific community it means little. Lamborghini cries Prestige to race car fans but for people who use cars to drive from point A to B only it means nothing. Same goes with prep school prestige. It means something only to those who have knowledge and experience with them (colleges, for example, that have worked with different schools for a long time). To them, my guess is that a number of schools are at about the same level in the prestige barometer, and I agree with other posters that Deerfield and Lawrenceville are certainly in the same league, so prestige shouldn’t be a factor in this decision making process.