In Guatemala City, dozens of people have been injured in clashes between police and students. The students were protesting an education reform that would extend the curriculum from three to five years. Forty students were taken to the hospital. The country's Interior and Education ministers were also injured.
But, of course, those involved in the protests were not just students. There were people with hoods who had infiltrated and manipulated the crowds. They were very aggressive towards the security personnel which is not normal.
I'm sure that it is possible that individuals were manipulating the crowds so that they became more violent towards the security personnel. However, given the country's history, it's just as likely, perhaps even more so, that they covered their faces so as not to be identified by the police and to not suffer the same fate as have other protesters.
Colin at Americas North and South has more on the proposed educational reforms in Guatemala.