I didn't read all the replies but it's around this age where kids start to hang out with the wrong crowd.
What I mean by that is that Straight A students are considered "losers" and its "cool" to be failing. He probably brags to his friends that he failed this, or failed that. I would have a serious talk with him to clear this up. I've had friends with high IQ's and great potential almost fail out of school because they fell into the peer pressure of the "stupid" kids. By stupid kids, I mean the kids who really can't get an A in anything and degrade the kids who do.
It sucks that its such a young age. I saw this around 7th grade or so when I was a kid but high school fixed all of that. Once I was in honors courses with other smart kids, I developed good friendships where you excelled and competed for the best grades. No longer was failing "cool" but looked terrible. Get him through these next few years and make sure he gets accepted into honors classes and he will excel, trust me.
btw, this is advice from a male (it's MUCH more common among males) who went through this same thing and had some rough years in middle school and managed to graduate into an engineering program and graduate with a great job. Don't let one year of his life worry you.