How do you handle followers you get through Leadership?

[Halivar]

Now, as I recall, creatures summoned by Summon Monster et al don't grant experience when killed. The rationale being it's a spell, therefore part of the caster.

So, do followers and cohorts give experience? After all, they're part of the character with the feat.

Followers do not. Cohorts do, but at half experience. Basically, for any encounter, divide the xp by (character * 2)-1 and give the cohort one share while everyone else gates 2 shares.

For instance, 4 PC's and a cohort gain 9000 xp, collectively. (5*2)-1 = 9. 9000 / 9 = 1000. Thus, each PC gets 2000 xp, while the cohort get 1000 xp.

EDIT: I belatedly realized that I did not answer your question. Rather, I answered the wrong question. Whether or not anyone other than the PC counts towards experience is the DM's call. The DMG seems to be silent about this.