About 120 soldiers are patrolling streets around schools in Acapulco's rougher neighborhoods, but that hasn't persuaded many of the schools to reopen after receiving extortion demands and threats.
Some 460 schools have been closed since late August after banners, handwritten signs and other threats had demanded that teachers hand over part of their pay as protection money.
The Guerrero state government reached an agreement last week to reopen the schools Monday, in exchange for increased security measures.
A state government spokesman says 90 percent of the schools had reopened but acknowledged that classes were not being held in many of them. Acapulco has been the scene of bloody drug cartel turf wars.