MEXICO CITY (AP) — Mexico’s Senate overwhelmingly passed a sweeping reform of the notoriously dysfunctional public school system early Wednesday, handing President Enrique Pena Nieto an important victory in his push to remake some of his country’s worst-run institutions.

The Senate voted 102-22 in favor of a standardized system of test-based hiring and promotion that would give the government the tools to break teachers’ unions’ near-total control of school staffing.

That control includes the corrupt sale and inheritance of teaching jobs and it has been widely blamed for much of the poor performance of Mexican schools, which have higher relative costs and worse results than any other in the 34-nation Organization for Economic Cooperation and Development.

"The inheritance and sale of jobs has ended," Education Secretary Emilio Chauyffet said on Twitter. "Merit is the ideal means of access to, and progress in, a teaching career."

The late-night vote clears a path for Pena Nieto to move forward with a series of even more controversial reforms, including a measure that would violate one of modern Mexico’s longest-standing taboos by allowing private investment in the state-run oil company.

But there is potential trouble ahead.

Education advocates say a series of concessions to the smaller of the two main teachers’ unions undermined the reform’s ability to create true change in the national education system.

And despite those concessions, the smaller teachers’ union has promised to continue days of debilitating protests in Mexico City, and to throw its support behind a weekend protest against the oil reform by leftist leader Andres Manuel Lopez Obrador.

"When Congress is rendered void, the only thing that remains is the streets," leftist senator Mario Delgado said as a series of his Democratic Revolution Party’s objections to specific measures of the reform were rejected in relatively narrow votes.

The education reform initially pitted Pena Nieto against the country’s main teachers’ union — Latin America’s largest union and once one of the most important allies of his Institutional Revolutionary Party. The union, known as by the Spanish acronym SNTE, fell into line after its head, Elba Esther Gordillo, was arrested on corruption charges in February. She remains jailed pending trial.

A smaller, dissident union known as the National Education Workers’ Coordinator, or CNTE, continued protesting and eventually rallied thousands of teachers from poor southern states, paralyzing large sections of the capital for more than a week.

In the end, the CNTE won a series of concessions that help protect its members. Reform advocates said the concessions also could undermine the push to improve Mexican schools.

Much of Mexico’s educational dysfunction is attributed to the relationship formed more than a half-century ago between the Institutional Revolutionary Party and the teachers’ unions, which gained increasing control of the education system in exchange for throwing their strength behind the government in the voting box and on the streets.

Over the years the unions developed a virtual lock on teacher hiring and promotion. Almost every new teacher must go through a union to gain a school assignment, a practice that has spawned notorious levels of corruption, including the sale and inheritance of teaching positions.

Particularly in states with schools controlled by the CNTE, critics say, union influence has transformed schools from educational institutions into mechanisms for extracting funds from the state. The CNTE has become notorious for threatening elected officials with debilitating strikes and marches in order to maintain and increase benefits that make teaching one of the primary sources of legal income in much of rural Mexico.

Mexico today spends a greater share of its budget on education than any other member of the OECD except New Zealand. Out of that budget, the country spends more than 90 percent on staff compensation, again higher than any other member of the OECD. That spending doesn’t translate into better results or smaller class sizes, however. Only 47 percent of Mexican children graduate from the equivalent of high school and Mexico also has the OECD’s highest student-to-teacher ratio — 25 pupils to every teacher, on average.

Among the benefits ended by the educational reform are payments of more than $100 million a year by some estimates to thousands of teachers who work full-time as union organizers and rarely, if ever, set foot inside a classroom. Education reform groups have found some union representatives earning hundreds of thousands of dollars per semester.

The rest of the reform focuses on reasserting government control by awarding teaching jobs to the highest scorers on a standardized test instead of funneling them through the teachers’ union, a measure weakened by a series of back-room compromises with the CNTE.

The law maintains union control over the current crop of teaching students by delaying test-based hiring for two years. Serving teachers will have three chances to pass an annual performance test. If they fail all three, they will be moved to an administrative job or given the chance to retire instead of being fired. In another compromise, failing teachers can appeal transfers to local labor law magistrates, a measure that reduces federal control in favor of local officials more easily influenced by the teachers’ unions.

The law was also weakened by a measure that classifies individual teachers’ test results as private, personal information, angering reform advocates who said that broached a key promise to empower parents by giving them more information about their children’s schooling.

With the education reform headed to Pena Nieto’s desk, still pending are the oil reform; detailed reform of the country’s weak tax laws; and strengthening of its telecommunications regulations, which have allowed two families to control most of the multi-billion dollar market while charging prices, particularly for phone service, that are well above global norms.