Complex sentence: One day, however, she overhears C.T. helping another student with arithmetic, revealing to her that despite his stubborn refusal to participate in class since returning to school, he has actually been continuing to learn.
Split into simpler sentences: One day, however, she overhears C.T. helping another student with arithmetic. This proves that despite his stubborn refusal to participate in class since returning to school, he has actually continued to learn.