At Kenmore Middle School in nearby Arlington on Monday, President Obama instructed students to do as he says, not as he did back when he was a trouble-making middle-schooler. "I've got a confession to make," Obama said. "This probably is right about the time I was at my worst. I was getting in trouble all the time. I was in the principal's office all the time." Obama's teen-aged misadventures have been well chronicled in his memoir "Dreams of my Father," and they seemed to last well into his college days. At Occidental College in the ’80s, Obama apparently picked up...