Much-ado about nothing

A colleague had to swap a period of lesson with me to go through a paper with my English class.

I went over to her high-ability class, not knowing what I could do with them. Exams were over and I did not teach them in any subject.

I was somewhat relieved when I saw the colleague who was not the class' subject teacher either walking out of the class.

I asked him, hoping to have something for the children to do,"What did you do with the class?"

He replied nonchalantly,"What they have been doing."

I was a little surprised, since exams were over,"Oh, what have they been doing?"

He quipped,"Nothing."