I think there are a number of reasons he is nervous. One is because there were two kids in his class last year who, despite multiple complaints and meetings with the teacher, made life absolutely miserable for him last year. I can't be sure where the fear of failure came from (other than the fact that he does tend to be a bit of a perfectionist). But my suspicion is that it was a product of two things: When he was in first grade, he took second grade math. But when he reached second grade, the schedule would not allow for him to go to third grade for math. So for 3/4 of the year, they made him do second grade math all over again! Not only the same material, but the same worksheets! He came home one day in tears because he thought his teacher believed he was stupid, and that was why they were making him do this. (I have already spoken to all of his teachers, administrators, and guidance counselor and made it clear that this year is going to be different). The second event that may have made him nervous is that NC schools put a huge emphasis on End-Of-Grade tests, and this will be the first year he has to take them. Last year, when they were getting ready for the tests, the teachers spent a lot of time warning them that third grade was far more difficult so they have to work really hard, and informing them that the world was going to end if they failed their EOG's.
I'm no psychologist, but it seems pretty clear to me that these things probably affected his worries about school. I tried the approach of following through with his fears last night. He was worried that he wouldn't learn anything in school (seems incompatible with the fear that he wouldn't be able to do the work, but in his mind, it worked). So I asked him what would happen if he didn't learn anything in school. He was silent for a long time, then said, "Oh, I guess it doesn't matter, because you can teach me stuff at home!" Then he was happy for a couple of hours, before he found the next thing to worry about.