Jake Porter is 17, but he can't read, can barely scrawl his first name and often mixes up the letters at that. So how come we're all learning something from him? In three years on the Northwest High football team, in McDermott, Ohio, Jake had never run with the ball. Or made a tackle. He'd barely ever stepped on the field. That's about right for a kid with chromosomal fragile X syndrome, a disorder that is a common cause of mental retardation. But every day after school Jake, who attends special-ed classes, races to Northwest team practices: football, basketball, track....