Six years ago, after being elected to the Mexican presidency by the narrowest of margins, Felipe Calderon declared war on the country’s drug cartels. Now, with Mexicans heading to the polls on 1 July to vote for his replacement, the political debate is understandably dominated by the spiralling violence unleashed by this war, in which 50,000 people have died.

Nonetheless, the cartels are far from being Mexico’s only problem: the country’s education system, for example, is crumbling and bedevilled by persistent underperformance. Yet just one of the presidential candidates, Gabriel Quadri, has treated this issue with any seriousness, while the front-runners have tried to avoid it.

Yet why is such an acute problem being overlooked? In the latest education report from the Organisation for Economic Cooperation and Development, Mexico ranked bottom of 34 countries in student performance. The system is rife with underqualified, and even unqualified, teachers. Extraordinarily, many teaching jobs are bought, inherited or handed out through patronage. A recent survey showed that only 16 per cent of teachers got their jobs through open competition, while 20 per cent got them through union contacts, 5 per cent inherited them and 1 per cent paid for them.

It is therefore unsurprising that poor student performance is mirrored by that of the teachers. In a 2008 teacher evaluation, a staggering 80 per cent of teachers failed to achieve an “acceptable” rating.

As a result, Quadri - who is standing for a party firmly rooted in the education sector, the New Alliance (Nueva Alianza) - is basing his central campaign around a revolutionary, teacher-led overhaul of Mexico’s education system. But as so often happens in public life in this central American country, it is far from being as simple as that sounds.

Behind the scenes of Quadri’s campaign is the diminutive but imposing figure of Elba Esther Gordillo, known in Mexico as La Maestra (The Teacher). The 67-year-old Gordillo is the president-for-life and “moral leader” of the National Education Workers’ Union (Sindicato Nacional de Trabajadores de la Educacion: SNTE), Latin America’s largest union - and one of its most powerful.

The SNTE created the Nueva Alianza in 2005 after Gordillo was forced out of her position as the congressional leader of the Institutional Revolutionary Party (Partido Revolucionario Institucional: PRI), which effectively governed Mexico as a one-party state until 2000.

Despite being a founding pillar of the party, the SNTE has never previously backed a Nueva Alianza presidential candidate, preferring to cut deals with other parties. And with Quadri trailing badly in the polls, La Maestra and the union are in danger of losing their reputations as presidential kingmakers, earned through their political manoeuvring in previous elections.

Gordillo’s story is an extraordinary one. Her mother, Estela, was one of 41 illegitimate children fathered by a rich distiller in rural Mexico. Disowned after a marriage disapproved of by her father, Estela was widowed and struggled to raise her children on the meagre wages of a public school teacher. Since then, Gordillo has reportedly amassed a vast personal fortune and is said to own properties in Mexico, California, England, France and Argentina, as well as a yacht and two private jets. To say she has exerted an iron grip on the SNTE since assuming the leadership in 1989 would be an understatement.

She has been dogged by allegations of bribery, extortion, embezzlement, intimidation and influence-peddling and was even accused of organising the murder of a political rival in the 1980s - although the death was investigated and Gordillo was never charged.

In July last year, Miguel Angel Yunes, a one-time ally of Gordillo and former head of the social security fund for state workers, publicly alleged that four years earlier he had refused Gordillo’s demand to be paid $2 million (pound;1.2 million) a month from the fund to finance the Nueva Alianza. “Elba Esther’s only interest in life is power and money,” he said. “She is like a kind of King Midas. Everything she touches she corrupts.” In a written statement, Gordillo described the accusation as “rash, frivolous and slanderous”.

Yet despite the scandals and allegations, no charges have ever been brought against Gordillo. Instead she has accumulated enormous political power for herself and her allies. In Mexico, both those in power and those who aspire to it have had to court La Maestra, wary of her ability to mobilise the SNTE’s 1.4 million members and their votes. It is easily the single biggest obstacle to reform of the education system.

The SNTE has traditionally worked closely with the PRI, but after the 2005 split, Gordillo struck a deal with Calderon, then presidential candidate for the rival right-wing National Action Party (Partido Accion Nacional: PAN). In a vote tainted by allegations of widespread fraud, Calderon eventually won the 2006 presidential election by just over 200,000 votes - a margin of 0.5 per cent. According to Gordillo, in return for the union’s support, Calderon placed her allies, including family members, in key education government posts. The consequence was six years of stalemate as the education minister and current PAN presidential candidate Josefina Vazquez Mota repeatedly clashed with La Maestra and her allies.

The children come second

This relationship between the SNTE and the government has allowed the union to maintain a stranglehold on the education system and it retains tight control over the curriculum and over the training, hiring and evaluation of teachers.

Journalist Carlos Loret de Mola recently produced a documentary on the failings of the Mexican education system called De Panzazo (slang for “barely passing”). “It is a type of dialogue and submission between the public political power and the power of the teachers’ union,” he says. “The education system is governed by adults, dominated by adults and installed in order to satisfy a series of needs of adults. Without any thought for the children, (the union) look to conceal, they look to cover up (and) they look to block,” he adds.

Given the profession’s chronic underperformance, it should not come as a surprise that teacher evaluation has been a key battleground between the SNTE and reformers and, until recently, the SNTE has managed to block all but the most superficial reforms. A new agreement will introduce universal evaluation for the first time, but its implementation has been long delayed.

The SNTE is also often blamed for the poor returns on investment in education. While Mexico invests more in education as a proportion of public spending than any other OECD country, thousands of schools need serious repairs, face electricity blackouts or have no running water. Almost 95 per cent of education spending goes towards teacher and administrative salaries and benefits, some of which pay for teachers who don’t teach. A recent initiative called “Where’s my teacher?” identified more than 21,000 teachers who were working for the union or the Nueva Alianza while being paid by the state as teachers.

“In Mexico, education is not seen as working for the learning of children,” says Loret de Mola. “Instead, it is working for the enormous quantity of money that it represents and that is divided among very powerful people.”

However, for some experts, the union is a useful scapegoat and a distraction from the failures of politicians - the “perfect excuse”, according to Armando Chacon from the Mexican Institute for Competitiveness. “While acknowledging the negative effect this union can bring, to blame the union for the failure in education in Mexico is childish,” he says. “It is ridiculous - it is saying that while this union exists there is nothing we can do.”

Chacon also believes the debate over quality of education obscures a much larger problem that can be resolved without clashing with the union. The latest OECD figures show that Mexicans spend an average of just 8.8 years in education - compared with 13.3 years in the US and 12.6 years in the UK. According to education thinktank Mexicanos Primero, only 62 per cent of Mexican children finish primary education, with 45 per cent completing secondary and just 27 per cent leaving school with a qualification comparable to UK further education. Approximately 13 per cent graduate from university and 2 per cent go on to postgraduate studies.

However, with the other presidential candidates keen to place the blame for Mexico’s failings on the SNTE and Gordillo, Quadri has faced heavy criticism for his intention of working closely with the union - criticism that Chacon believes is hypocritical. “All these parties have looked for the support of this union and they have legitimised that senora in her position. Quadri’s sin is a sin that all of them are guilty of,” he says. “You can’t try to fix this union from outside the union. I don’t support it in any way, but. it is with these teachers and this union that they have to build the solution.”

With Quadri a distant fourth in the race, polling at around 1 to 2 per cent, his plans for reform are likely to remain unfulfilled. At the start of the current campaign, the SNTE looked set to reforge its alliance with the PRI, and it was only after negotiations broke down that Quadri received official backing. Having opened up a lead of 13 percentage points over his nearest rival in the latest polls, PRI candidate Enrique Pena Nieto now seems almost certain to take the presidency without having to resort to bargaining for the union’s support.

“The PRI don’t want to and don’t need to arrive in government with this weakness,” says David Calderon, director-general of Mexicanos Primero. For him, this is a mark of the SNTE’s waning electoral influence - and the small possibility that some kind of educational reform may be in the pipeline. “It is not like it was in the past when the union could openly tells its members to vote for one candidate and control with discipline what happened,” he says.

Quadri, meanwhile, insists that he can win the election and on his campaign’s independence from La Maestra and the SNTE. When students questioned him on the subject at a university appearance, he denied having any relationship with Gordillo, ”.although you don’t believe me, although you laugh”.

Most Mexican voters would say that this is the same for just about any other politician, too.