Doesn't make much difference to your promotion prospects. So don't worry if you don't get it. Most of the classes leaders I knew thought they knew it all most turned out to be mongs. That's in my experience many years ago
From my experiences as a member of staff at Raleigh (a few years ago), two types of recruit get made class leader:
1 - The very good, responsible, sh1t-hot high flyer who will get promoted anyway. This is to make sure the class get to where they are supposed to be, in the right rig and at the right time without us getting hassled.
2 - The total divvie. This is to give us a reason for having them screw up big time, get put on warnings quickly and DUDT. I appreciate that this is not possible now, but I'm talking about a few years ago prior to Deepcut.