L.,
Nice sense of humor! (oh, the torture of homework!)
There's a great article in the New York Times magazine on children and their perception of what it is to "be smart". Here's the link:
http://nymag.com/news/features/27840/
In my work with children, I found this Po Bronson article exciting and right on target. A revelation that goes against what we know as parents: when we keep telling our kids that they are smart, they begin to actually avoid challenges, because they believe that it is their 'smarts' that matter and not the hard work of learning. I hope you take the time to read this, because it verifies everything I've seen as a nanny and preschool teacher.
So your statement "I think he is a bit of a perfectionist so when he doesn't get something right away he is immediately frustrated." is on track.
And this is nothing to beat yourself up on as a parent, telling your kid he's smart. We just might want to rephrase our praise to focus on his efforts instead. That it isn't just about the 'materials he has on hand', it's about the work he does to learn.
In regard to why he can't answer your questions regarding what's behind his upset: Bruno Bettelheim writes in "A Good Enough Parent" that it's wise not to ask children "WHY" questions. They usually do not have the psychological objectivity to know why they feel the way they feel, and may be worried about giving us a 'right' answer which doesn't feel correct to them. (Because they have no idea where so many of their feelings are coming from.) Then, they might try to give us an answer which seems reasonable to us, but might feel like a lie to their own selves. You might consider less ethereal, more specific questions: "What do you think will happen if you try this new assignment?" "Where does this feel tricky for you?" These are questions he'll feel more emotionally confident in answering. Even "What do you think will happen if you don't get this right?" is going to give you, as a parent, more helpful answers, and these don't go into that confusing emotional realm that a 'why' question might.
One last suggestion is to sort of ignore the tears, give him a hug, and go about what you need to be doing with an "I'm here when you are ready for my help." That will also let him know that you will be available, but you break the cycle of giving lots of attention for tears. It puts the ball in his court to sort of pull it together and get on to the task at hand. I hope this doesn't sound harsh, it's not meant to, it's just that when we have a pattern of getting upset before doing something new, it's nice to change it. The discussions regarding his emotions are distracting from what he needs to be doing, which is his homework. A kiss, and an encouraging word will give him a nice message of confidence that YOU believe he can do it.
Oh, and how did the conference go that you'd posted on last week... just curious. :)