I don't really get too deep into the psychology of much of anything, but I do wonder if it has anything to do with birth order. There are tons of books out there that deal with how a first-born is treated and acts differently than a middle-child, an only child, and a youngest-child.
Of course, that psychology was flipped backwards in my family.
But, in reading your message, I wonder if it is part personality, part birth order, and partly how you may react and treat them differently (subconsciously).
As a mom of 2, I can see that I inadvertently do it with my kids. They have different personalities, are at different stages though both still really young, and have faced different circumstances so far in life.
My best advice is to sit down with him, tell him that you're sorry you get frustrated, explain what he does that is frustrating to you and ask how you can best help him. As a professional, I've been amazed at how many people in management approach their employees with a one-size-fits all approach when in reality everyone is motivated a little differently.
If he were my son, I'd spend some time one-on-one just trying to understand him: what makes him feel good, what frustrates him, what challenges he has with school, what he likes to do, what he'd really like to avoid, etc.
Then, I'd tailor my parenting slightly based upon his feedback to see if you can work on motivating him a little more towards what you're desiring based upon who he is - albeit different from how you approach things and other children you may have.
Good luck! I hope you get on the same page with him soon.