One afternoon last summer, one of my students, Miguel, had stopped by my house randomly to say hello. His family lived in the neighborhood and he'd been walking by, he said. Miguel had always been a nice kid, nobody I'd ever had any trouble with, but from the moment he showed up on my doorstep, there was this nervous tingle in the back of my mind about that tiny remote possibility of someday sitting in a courtroom trying to reassure a jury about a no-witness encounter with a student in my home. Miguel hadn't made it past the front steps, and that was a student who had never given me...