Okay, this played out in my head last night, with a minor change.

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Rebecca knew she wouldn't be able to leave the house again that night until her homework was finished, so she resigned herself to waiting until tomorrow to talk to Gillian.

After a long, busy day with no classes in common, Gillian and she finally had their last class together. It was history, with old man Campbell, but at least he did most of the talking and they didn't have to pay attention. At long last, class was over.

Fiddling around with their books and things, Rebecca and Gillian managed to stay behind when everyone else had left. It was late on a winter's day, so it was already getting dark outside. The lights were off in the room, so no one would know they were still in the classroom.

Moving to the front of the room, Gillian had a million questions racing around in her brain, and was trying to ask them all at once.
When Rebecca had finally told her the whole story, Gillian just gaped at her in shock. The shock slowly gave way to disbelief.

"Are you sure that all happened?" she asked doubtfully.

"Yes," Rebecca insisted. I still have the red marks on my bum."

"Really?" Gillian's voice was full of curiousity. "Can I see?"

Before Rebecca could say another word, the light flicked on, and Mr Campbell walked into the room. Locking the door behind himself, he sauntered towards the scared girls. "Yes, Rebecca, I'd like to see these marks too."