MEXICO CITY – President Enrique Pena Nieto signed Mexico's most sweeping education reform in seven decades into law Monday, seeking to change a system in which teaching positions could be sold or inherited, and no official census of schools, teachers and students was ever carried out.

The legislation, which is widely expected to weaken Mexico's powerful teachers' union, was approved earlier by congress and the majority of state legislatures. The reform was a plank of a pact signed between Pena Nieto's Institutional Revolutionary Party and the two main opposition parties

It seeks to create a system of uniform standards for teacher hiring and promotion based on merit, and will allow for the first census of Mexico's education system.