India arrested a teenager on Wednesday for allegedly slitting the throat of a seven-year-old schoolmate in hopes the murder would lead to an exam being postponed, federal investigators said.

The 16-year-old is accused of killing his young schoolmate in September at a smart private school near Delhi in an attempt to delay an impending test and parent-teacher meeting.

Police had initially detained a bus conductor over the murder, claiming he killed the boy after the young pupil resisted a sex attack.

But a spokesman for federal investigators said they had credible evidence against the “academically weak teenager, whose motive was to postpone the examination and a forthcoming parent-teacher meeting”.

“He admitted during questioning that he wanted to shut the school to defer the exams and meeting,” Central Bureau of Investigation spokesman R.K. Gaur told AFP.

The teenager, who cannot be named for legal reasons, would be sent to a juvenile detention centre until his trial for murder, he added.

Gaur said the bus conductor would remain in custody until cleared by a court of any wrongdoing.

The crime made national headlines and stoked concern among parents over safety in schools.

India's swelling middle class has fuelled the growth of private schools in a country where public education is under immense strain.

Much prestige is placed on academic achievement and children face intense pressure to score good grades.

Experts say this has aggravated stress and mental illness among teenagers.

India, a nation of 1.25 billion, has the world's highest rate of suicide. Students are particularly vulnerable. Official figures show nearly 9,000 students committed suicide in 2015.

Health experts say many young people find it difficult to cope with the pressure to succeed and struggle to accept failure in examinations.