Quote Originally Posted by Padfoot Patronus
I agree with Elf about Sirius' lineage being an important factor in Slughorn's mind to make him a part of the Slug Club.

I think he accepted Ginny because he was impressed by her timely spell and for her bat-bogey being a very good piece of magic. If this is true for Slughorn's general recruitment criteria, then it is possible that Slughorn be impressed by good wand-work in the numerous pranks the Marauders' played at Hogwarts.

- Akay
What I meant was that causing trouble does not exclude you from being in the Slug Club. I think that James coming from a wealthy family would be enough reason for Slughorn to invite him into the club. Of course whether he and Sirus would go is a different matter.