I am a mid-level developer and leading a project at my company. I am very strongly encouraged to pair with another dev who is relatively new (half a year now). He is a good guy, but working with him can be very slow. When we pair everything takes about 3 times longer. If I split a large task into smaller bits so that we can work in parallel and ask him to do one of them, usually an easier one, he ends up taking way too long, and I end up helping him again.
Now to be clear, I'm not opposed to pair programming. I realise that it's ok to be slower for a bit if it means bringing a new dev up to speed. But it's been some time now, and it's not getting much better. I am struggling however to bring it up to my boss because I can't quite find the words that won't sound arrogant. I don't want to shoot the guy down, I actually quite like him, and I know my boss thinks he has good potential. So if I say plainly "This guy is slowing me down quite a bit", I know it won't come across well.
I know it's not strictly my job to train the guy. In fact, I'm not even officially leading the project (it just kind of happened that I'm de facto leading it), so I can't even say to my boss "my project is failing because of this guy". But I want to do the right thing, not just the minimum required thing. And the fact is, I need to address it one way or another, I want to finish the project soon + I'll start looking bad because of the delays. I want to do it in a nice way to not offend the dude and not to come off arrogant. Please help me find the right words.