Here is an NYT article about teenagers delaying their back-to-school shopping until a week or so after the beginning of the new year. Several independent sources, including some teenagers themselves, suggest that this is because kids are scoping each other out during a test period to see what everyone else is wearing at school, and then afterward making their choices based on that.
If the consumer behavior is new, then so must be the underlying motivation. When I was in middle school, I certainly don't remember that mindset myself or among anyone else I knew. You bought some new clothes and just hoped that you would look cool on the first day back from summer vacation. Compared to what they're doing now, it was more of a risk-taking approach.
Kids these days are definitely more conformist and afraid of taking risks, so I wouldn't dismiss the inferences of the article. I'd be interested to find out when this trend began. The article says it's been going over the past several years, but I'll bet it goes back to the mid or late 1990s, when young people started (just started) to get a lot more uptight and hive-minded. It's too bad that news articles rarely seek to trace anything farther back than 5 years ago.
It'd also be neat to see if people said this about when the Silent Generation when back to school in the '40s and '50s, compared to the more daring, wanna-stand-out way people dressed in the Roaring Twenties. Wouldn't be a surprise, but I can't get interested enough to pursue it any further than throwing it out there. Sometimes I wish I had a chick sidekick to look into stuff like this, or write up what I'd looked into. (I did read a couple short books on the history of jewelry, but haven't gotten bitten by the bug to write it up yet).