Take him back to the temple and see if he has passed any of them, I thought I still needed more influence but he became a monk when we chated the head guy.
There are several options in that conversation where he wants to think about it. Save and try the others to see the result, one of them should make him a monk with no thinking, hehe.
OK, so I finished the game - and found myself using Khelgar *all* the time ... at first he was dying a fair amount, but towards the end, in the last 'section' he was standing alone with me much of the time ...