A new report reveals that 92% of girls aged 12 to 17 who are living informally with a man - often a decade or more older - have dropped out of school.
Hundreds of thousands of girls in Mexico are missing out on education after getting married or living with a man - who is often much older.
New research shows that 83% of married girls under the age of 17 have left school, rising to 92% of those living informally with a man. But only 15% of those not in a live-in relationship have dropped out of school.
The report also reveals:
- There are 320,000 girls aged 12 to 17 who are in "early unions" or informal cohabiting
- Almost 70% of them are living with a partner who is at least 11 years older
- 25,000 girls aged between 12 and 14 are living in “early unions”
Child marriage forces millions of girls out of school every - especially in developing countries where more than 60% of child brides have no formal education.
An average of 40,000 children and young women under the age of 18 are married every day, about 15 million each year.
Early marriage increases the risk of girls suffering violence, health complications and death in childbirth.
The legal minimum age for marriage in Mexico is 18 - but United Nations officials say this isn’t being enforced in some states, where girls as young as 14 are allowed to marry.
Child marriage in Mexico is largely driven by poverty and tradition, according to the charity Girls Not Brides.
In two of the country's federal state studied for the report - Chiapas and Oaxaca - being in a live-in relationships is "almost synonymous with being out of school". Only one in 20 girls age 12 to 17 in a union there still attends classes.
The report says: "In the impoverished indigenous communities of Chiapas, Oaxaca and Guerrero, where nearly all rural unions are non-formal, most unions involve some kind of courtship and agreement between the girl and the boy."
In the wealthiest states the school attendance rate among girls in unions is still low - 16% to 21%. Across the whole country, 40% to 55% of girls aged 12 to 17 in unions have had at least one child.
Across Latin America as a whole, nearly one in three girls are married off before they are 18. In many countries, children can get married under 18 with the permission of parents or a judge.
Luis Almagro, General Secretary of the Organization of American States, recently promised to tackle child marriage in Latin America.
“With one in five girls married or living in informal unions before the age of 18, we are losing entire generations to poverty, discrimination and violence,” he said.