Project Runway LOLs

Someone explain to me why the designers on last night's Project Runway giggled when their high school aged models came out for the prom-dress challenge? I mean, shouldn't they get used to dressing 15 year olds, or even 12 year olds? Even Judge Micahel Kors used a 16 year old in his latest ads. Oh wait, only chubby teenagers with normal cheekbones are lol-inducing. Think back to your high school years and confirm that for yourself.