Answer:
That he hasn't practiced his reading. He also realized that he didn't know the meaning of some new words.
Explanation:
In the statement "When he is told to read in class, what does panchito realize..." Panchito has to read in class but he couldn't read appropriately because he had not practiced enough. Then, Panchito discovered some unfamiliar words in the text. As a result, Panchito felt disturbed when he was trying to read aloud.
