Is this a hen or a rooster?

[babybaits]

My son recently started raising chickens. He bought 4 white leghorns. He was told that one of them was about 4 weeks old while the other 3 are around 3 weeks old. He's slightly bigger than the others, but I've realized that his comb is also a lot larger than the other ones. I've never been around chickens until now, but I wouldn't think that 1 week would make such a difference in the size of it. It's even larger than other chickens that he has, which are about 2-3 months old, but not leghorns. Would someone be able to determine whether this is a hen or a rooster? The second picture is of 2 of the other ones.

 

[AmeraucanaHank]

ya, I think he's a male.