Passage Summary: Putting kids of different ages in the same class used to be a disaster, but nowadays it's actually helping everyone learn better.

Reasoning: Historically, mixed-age classrooms failed because younger students were ignored and older students were bored, but modern versions of these classrooms are highly successful and stimulating for both groups.

Analysis: The paradox lies in the shift from failure to success within the same structural setup of mixed-age groups. We need to find a factor that changed between the 'past' and 'recently' to explain why the outcome is now positive. Look for an answer that introduces a new variable, such as a change in teaching methodology or curriculum design, that prevents the old problems of boredom and confusion. It is quite a turnaround for a system that used to leave everyone either lost or yawning.