Three of those arrested were former students of the school.
Four persons were arrested in connection with a bomb blast in a school in Titagarh area in West Bengal's North 24-Parganas district, a senior police officer said Sunday.
The accused, aged between 18-19 years, were picked up from Kamarhati and Titagarh areas around midnight, the officer of Barrackpore Police Commissionerate said.
"We are trying to explore all possible aspects by interrogating them. One of the arrested hails from Kamarhati while the rest are from Titagarh," he said.
The crude bomb exploded on the roof of the school building on Saturday when classes were in progress.
There was no casualty in the incident, as students and teachers were in rooms located on the first two floors of the three-storeyed building, police had said.
The officer said preliminary investigation revealed that the accused had changed their initial plan to hurl a powerful crude bomb at the school gate, as the spot was crowded.
They climbed onto the roof of an adjacent building to carry out the act, he said.
The officer said three of those arrested were former students of the school.
Personal enmity between the accused and some other students of the school was believed to be the primary motive behind the incident.
He added that 10 crude bombs were found during a search operation at the residence of one of the accused.
Meanwhile, the BJP demanded a National Investigation Agency (NIA) probe into the bomb explosion.
"I will put forth the demand (for NIA probe) to the Union Home Ministry on Monday," Leader of Opposition in Bengal assembly Suvendu Adhikari told reporters.
BJP state president Sukanta Majumdar, who also emphasised the need for a similar investigation, added: "Bengal seems to be the only state in the country where school children are targets for a bomb attack." Reacting to the comments, veteran Trinamool Congress MP Sougata Roy said the BJP has a habit of demanding NIA probes for every incident.
Earlier in the day, BJP national vice-president Dilip Ghosh said Saturday's development points to the fact that "even school students cannot feel safe in Bengal".
"The education sector has begun its final journey in the state under the Trinamool Congress rule... Youths are roaming around with pistols and bombs... as there are no jobs in West Bengal," Mr Ghosh claimed.
Countering him, TMC's Mr Roy said the police are doing its job, and investigation is underway.
"This should not be politicised by the BJP, which patronises miscreants," the Dumdum MP alleged.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)