Everyone has their own theories. He are a few of mine (if I did all of them you'd be Lesen this for days:P)

Theory 1:
Jason has been to one of the different camps before. Coach Hedge sagte something like, "I've never seen Du before in my life." Think about it, the mist, maybe? He may not know it, but he's tricking everyone into thinking he's always been there. This might be one of my stronger theories, because Hedge did mention that he was probably good with the mist because he's never seen him and Piper is his girlfriend and Leo is his bestfriend, though he has no memory of them.

Theory 2:
Percy was sent to find Jason, Piper, and Leo but something went wrong and now he's missing. What if Jason had been there the whole time and the gods made the coach forget Jason. And made Jason lose his memory so he can't help Annabeth. When he doesn't return, they sent Annabeth and Butch to get them after Annabeth's vision.

Theory 3:
Jason has two godly parents. Not likely, but who knows? He survived that lightning bolt, didn't he? From what we heard Dylan say, it would have killed him and around 20 others.

Theory 4:
Percy, Jason, and Piper's dad were together when all of this happened. Percy probably ended up somewhere with no memory, like Jason. And since we have another theory about Piper's dad being a demigod, he was the one taking them off to do whatever they were supposed to do.

Theory 5: (I changed this theory.)
Jason has been to camp before but Piper and Leo haven't. Jason learned how to trick people with the mist but he Lost his memory. Since Leo and Piper haven't been to camp, they can still be tricked Von the mist.

I have a lot more, and I'll keep on posting arcticles with theories and news.

Pai! (Peace in French)