Carl wandered back home slowly, and by the time he got back, his nine year old brother Mike was asleep. Carl slept in the next room over, so he tiptoed around trying not to wake him. It was late, so he just threw his pants and shirt on the floor and went to sleep.
He was woken up by his alarm going off, and then, to his surprise, a loud thumping noise. He sat up in bed, and saw Mike through the bars of a bunk bed. Looking around quickly revealed him to be in his brother's room, although it looked slightly different, and lying in a bunk bed. Somehow his boxer shorts had been replaced by green and white checkered pajamas, similar to ones his brother owned.
Carl jumped out of bed and ran to the bathroom, despite his brother calling out, "Hey, it's my turn to use the bathroom first." When he saw a boy almost identical to Mike reflected back, his jaw dropped open.
Mike banged on the bathroom door. "Carl, it's not fair! I get to use the bathroom first today!" Carl let him in, and while Mike was showering, hunted around trying to figure out what had happened. His own bedroom appeared to have been converted into a study, while Mike's now had a bunk bed and otherwise appeared prepared for two boys. A quick glance at pictures around the house revealed that the two had somehow become twins.
When Mike came out of the shower, Carl asked, "How long have we been twins?" Mike looked at him oddly. "Um, nine years. Since we were born, dumb ass."
Figuring that once he got to school, he might be able to figure things out, he showered and dressed. The clothes were a little childish, the sort of thing Mike wore, but he couldn't find any of his own clothes. On the hand, he did seem to remember exactly where all of his new clothes were.
They were driven to school, and Carl followed Mike to his (their, now) classroom. The room looked familiar, and he recognized the teacher, and even remembered where the desk was. Looking around the room, he recognized the other kids as well. He realized that he somehow knew which ones were his friends, which weren't....he began to worry, and tried to recall being eleven. No, thirteen. He had been thirteen before, and had been friends will Joey, who was sitting next to him...no, that was a new friend...
By the time class had started, he got everything sorted out. He was nine, he was in his classroom, sitting right behind his twin brother.