Why are all the students writing Da-Zi-Baoa?

In Chapter Three, Chairman Mao denounces the education system and says its been poisoning young children's minds. This is the first big public statement that kind of started the Cultural Revolution. All the children in Ji Li class start making da-zi-bao's about the teachers and pasting them all over the school. One of them is made about Ji Li saying she had a relationship with one of the teachers and she is very upset. Chairman Mao successfully begins the students' rebellion against educators and educational institutions.