Riot police stand guard on the perimeter of the Interior Ministry building as teachers from Mexico's southern states belonging to the dissident teacher's union CNTE march during a protest against educational reforms, in Mexico City September 4, 2013. Mexico's Congress gave final approval on Wednesday to a government bill to overhaul an education system that badly lags global peers, despite teacher protests seeking to derail it.The Senate gave the nod to the final so-called secondary law of an education bill that regulates the tests that President Enrique Pena Nieto says teachers should take periodically to ensure they are up to standard. New teachers could lose their teaching jobs if they fail. [Photo/Agencies]