Link to short story that JKR wrote for charity is now on Leaky

[Zara]

> CJ: 
> The more we learn about James, the more I'm of the opinion the only 
> things distinguishing him from teenage Snape were better social 
skills 
> and a hot bath. James may have eschewed Dark Magic, but as he seems 
to 
> have found plenty of questionable uses for the good stuff I'm not 
sure 
> that's more than a technicality.

Zara:
Yes, that would seem to be the case. Young Sev may also have had a 
somewhat more intellectual bent. The difference is that James went on 
to join the Order, and Sev the Death Eaters, so that while James 
remained an arrogant jerk (that brief description is my opinion, 
naturally), he was an arrogant jerk on the right side.

I suppose that if this incident was between 6th and 7th years, and 
resulted in something more than a spectacular crash, it could be the 
reason Lily and Albus were impressed. Without this (or something 
similar) I would have to agree it is hard to see why he was made Head 
Boy.