What to Say
Here's what to say while touching him softly on the arm or shoulder, "You can cry and cry all you want, and I'm going to stay right here beside you as long as you're upset. Then when you're finished crying, you will need to complete your assignment."
Once he's stopped crying, offer him a snack and glass of water, then stay near him as he completes his assignment. Read your book, write a letter, pay bills, or do your own homework from your workplace. Your presence provides tacit control, keeping your child focused on the task at hand.
Refrain from looking over his shoulder and checking to see if what he's done is accurate. Show interest in his assignment but don't do it for him. Keep in mind the most important aspect in this situation is that the emotional outburst quiets and that he returns to a state where he can think and complete his assignment.
Can you take this loving yet hard-line approach? Only do so if you know your child if fully capable of the work, that it's not beyond his skill level and that his frustration is not stemming from a leaning disability. Taking this approach builds endurance for inevitable emotions that arise when academic challenges occur.