Bought this as a Christmas gift for my 11 year old son.  He's an average-sized 5th grader, but thin.  So I wondered if the size would fit him at all.  Turns out, the small is just fine - oversized, certainly, but in a way that is normal for kids (would hang to mid-thigh, if it weren't bunched up around his middle;  large around his chest/abdomen but not falling off his shoulders).

As a dedicated newbie Whovian, he loves it.  It's comfortable for him (and he is *very* sensitive to itchy tags, bumpy seams, uncomfortable threads - severe ADHD sensitive), attractive, appealing and fun.  Highly recommended!