Power leveling using a high level character in WoW?

I'd suggest letting him play at his own pace (unless he's an experienced MMORPG player starting WoW for a specific end-game purpose such as raiding / PVP). In particular if he's new to the genre, that first time exploring the world is such an amazing time, it would be a shame to be boosted through it.

Following the 'Shattering' the starter zones have had an overhaul and are fun to play through and also give a better step by step introduction to game mechanics and how to play your class.

Also the levelling speed now is pretty crazy - people in my guild are making jokes about being level 30 by lunchtime! It's not quite that fast, but if he gets into it he'll be 30 before he knows it.

Fwiw, your totem shouldn't impact his xp for mobs if you are out of the group. So if he tags them and they magma down, he should get full credit.

If you want to help someone at level 30, the best think you can do is usually get a level 30 of your own and quest together.