Gym class!

Alex stood for several seconds in thought, until he noticed that the classroom was empty. The teacher had taken no notice of his continued presence. "Oh, sorry!" He said as he quickly started grabbing his things.

"Hm?" asked Ms. Barnes, distractedly. "Oh, never mind," she said, as he rushed out the door of the class.

Alex was operating on automatic. He was ecstatic about the previous class, and was riding a serious high, but was not sure what to do next. He was headed to the next class, gym class, and the idea of what to do simply didn't occur to him until he reached the hallway with the girl's locker rooms.

By some quirk, the girl's locker room was on the main floor hallway, on the way to the stair to the boy's. Seeing three girls entering their locker room gave him the necessary inspiration.