According to school principal Deepak Rai, the boy did not report to classroom after prayer assembly in morning and went to toilet instead, where he allegedly poured petrol and tried to immolate himself.
After the sweeper noticed smoke bellowing from toilet, he alerted the staff and the boy was rushed to hospital.
"The teenager, has suffered 45 per cent burn injuries and been referred to Delhi's Safdarjung hospital, where his condition was stated to be critical," SSP Jaivir Rathi said.
"The boy had brought petrol in his water bottle. However, the reason behind the suicide attempt is not known yet," he added.