Teachers in government schools live in fear of the humble postcard.
In the hands of poor parents in the Indian capital who find that a teacher isn't listening to their complaints, the postcard is a powerful weapon.
"The parents are usually illiterate but the children write their complaint about the school on it and post it to a judge," said Ashok Aggarwal, the lawyer spearheading the "postcard campaign".
The campaign stems from desperation. Government schools are stinking slums. The toilets don't flush, the fans don't work despite the intense heat, each class has 120-150 children, and the teachers are too busy gossiping, knitting or playing cards to teach.
A survey in March by the NGO CRY found that 37 per cent of toilets in government schools were so dirty that children were forced to urinate in the open.
Complaints are invariably ignored. Fed up, Aggarwal hit upon the idea of handing out postcards to children in several neighbourhoods, urging them write to judges in the Delhi High Court.
About 300 postcards have been posted in the past few months in a campaign co-ordinated by voluntary group Project Why.
"When I used the teachers' toilet because ours was too filthy, I was beaten with a shoe and called dirty names," wrote Nitish Rana, a Class 8 student.
"My parents want me to do well but I can't."
Another postcard described the lack of clean drinking water and the almost continuous absence of some teachers.
"Even if a teacher is present, how can you teach 160 kids? Their idea of teaching is to write something on the blackboard and go off. They don't bother answering questions or explaining," said Project Why founder Anouradha Bakshi.
Stirred by the postcard bombardment, two judges have asked the Municipal Corporation of Delhi to explain the appalling conditions in schools. Jolted by the judges' intervention, the authorities have responded with small measures.
"In some schools, drinking water has appeared, the fans have been repaired and - wonders will never cease - the odd sweeper has come in to clean the place," Aggarwal said.
He says that neither teachers nor civil servants care about the schools because it is the poor - drivers, maids, cooks and street vendors - who send their children to them. "That's why they let principals do what they like. And the principals and teachers are not interested in teaching, only their salaries," Aggarwal said.
Meanwhile, teachers who have got wind of the postcard campaign are livid.
"They accused us of giving the children biscuits in return for writing the postcards. Some have threatened to fail them in the exams. So the children, unfortunately, are bearing the brunt of their anger," Bakshi said.