It was a flagship policy of Mexico’s president Enrique Peña Nieto: an ambitious reform programme that would revolutionize the country’s education system, improve standards, tame an all-powerful teachers’ union and crack down on rampant corruption – such as wages for non-existent “ghost teachers”.

Five years after it was launched, the plan has barely affected standards: Mexico still ranks last in education among the 35 Organization for Economic Cooperation and Development (OECD) countries.

And the ministry overseeing the reform has now been plunged into controversy after an investigation by the news website Animal Político revealed that last year, the public education secretariat (SEP) spent more money on communications than on teacher training.

A separate exposé in the newspaper Reforma found the SEP spent nearly 2,700% more on communications last year than was budgeted – even as rural schoolhouses were commonly left without roofs, electricity or water connections.

“This undermines the credibility of the reform,” said Marco Fernández, a professor in the school of government at Tecnológico de Monterrey.

Fernández added that the SEP did not spend what was budgeted last year for teacher development, but has exceeded its communications budget by a factor of 10 between 2013 and 2017.

The controversy has once again implicated the ruling Institutional Revolutionary Party (PRI) in a scandal at a time when educational reform has become an electoral issue before the presidential vote on 1 July.

The current frontrunner Andrés Manuel López Obrador has promised to kill the reform as he seeks to secure the support of teachers – important election organisers in rural Mexico where schools are often used as polling stations.

Former education minister and the current PRI campaign manager Aurelio Nuño defended the spending on communications, telling MVS Radio: “We launched a successful communication campaign that allowed [people] to better understand this great transformation.”

He added: “The education of Mexico’s children and young people is one of the main fights of this election.”

López Obrador has promised to increase public education spending, provide more stipends to students and introduce school lunch programs. He also said any future education policy would be made with input from teachers.

A poll published Monday in the newspaper El Financiero showed López Obrador receiving 46% support, 20 points over second place candidate Ricardo Anaya of a left-right coalition. Only 20% of respondents opted for PRI candidate José Antonio Meade.

Politics and education are intertwined in Mexico, where teachers were sent after the revolution to provide a state presence in remote rural areas and counter the influence of the Catholic church.

Just before the education reform was introduced in 2013, Elba Ester Gordillo, the powerful boss of the teachers’ union, was arrested on corruption charges, but she was released to house arrest in December – on the day the PRI forged an electoral alliance with a small party previously controlled by Gordillo and her union.