Students in Mexico are suffering from lack of education due to threats and extortions from high-profile drug cartels.
Children in at least 140 teaching centres have been left without lessons as teachers deemed it too dangerous for schools to open.
Educators have been targeted by drug gangs in recent months and have been threatened with death if they do not give up half of their wages.
Recent protest marches took place in Acapulco and teachers said they had had enough. But further developments have led to increased fear as severed heads were left outside of one school as a warning.
Elisabeth Malkin, who works for the New York Times, told CNN: "I think what has caught people's attention in Mexico is how the violence now has reached ordinary people, working people."
Messages to teachers have spread to Monterrey, another area where the Zetas drug gang is known to operate.
Cases of extortion have almost tripled since 2004 but the rise in threats to schools in the past month has caused many to shut their doors to protect the students and teachers.