Over the last two years, G Prakash Raj, a charity worker from India's Tamil Nadu state, has received hundreds of yellow postcards. Each reads the same.
Sent by a migrant child, the postcard informs Raj that the child is safely back home, and more importantly, back in school.
The postcard program was launched in Tamil Nadu in 2014 as a way of tracking the education of some of the more than 10 million children who are estimated to migrate with their families to different parts of India every year.
"When they are at work sites with their parents, we try and ensure they get basic access to education," said Raj, who works for Aide et Action, a non-governmental group which is collaborating with the education department to keep migrant children in school.
"When they head back to their villages six months later, they need to go back to school. Tracking that has been a big challenge," he told the Thomson Reuters Foundation.
Under the Indian Right to Education Act, every child between the age of four and 16 should be enrolled in school, but government data shows up to six million children aged between six and 13 are out of school in India.
Under the postcard program, the first to track the education of migrant children across state borders, migrant families working in Tamil Nadu are given a postcard when they head home.
They are required to get it signed and stamped by the principal of the village school and send it back to Aide et Action.
"In the postcard, the principal writes back to us saying that the child has been enrolled back in school. It's just a note but we are able to track a child's academics through it," said an official at the education department, requesting anonymity.
Last year, 547 postcards were sent back with migrant families from areas around Chennai and 495 came back saying that the children had been successfully enrolled in school.
To ensure the children are back in school, volunteers working with the education department travel to the home states and cross check enrollment.
Families who do not send back a postcard are traced back to their villages and counseled to enroll their children in school.
In Tamil Nadu, most migrants tracked are from the eastern Indian state of Orissa.
The success of the postcard program has prompted similar initiatives in other migration hubs across India, including in the neighboring state of Andhra Pradesh.
Although India's law allows children to go to any school in the country, an education department official said that a language barrier kept many migrant children out of school.
India, a country of 1.2 billion people, has 22 official languages and dozens more that are spoken across its 29 states.
"We are fixing that slowly," said the official, who declined to be named. "We are bringing people and books from home states to help the children in a language they are familiar with."
• Reporting by Anuradha Nagaraj, editing by Katie Nguyen. This story originally appeared on the website of the Thomson Reuters Foundation, the charitable arm of Thomson Reuters that covers humanitarian news, women's rights, trafficking, corruption, and climate change. Visit www.news.trust.org.