The body of the 14-year-old boy, a Class 9 student, was found dead with multiple stab wounds in the washroom of the school yesterday.
A police team from here has been sent to Valsad to bring the teenager to the city, he said.
He will be questioned to learn the reason behind the brutal killing of the Class 9 student, police said.
The accused student came under the lens after he was spotted in CCTV footage entering the washroom along with the victim, they said.
The victim had joined the school only a week ago and was staying with his maternal uncle here, while his parents live in Gujarat's Anand town, the police had said.
The killing was a grim reminder of the murder of a seven-year-old student in Gurgaon last year. The victim was found in a pool of blood, with his throat slit, in his school's washroom on September 8 last year.
Meanwhile, Jagruti Pandya, chairperson of the Gujarat State Commission for Protection of Child Rights, said the mental condition of the detained student will be examined to know what prompted him to allegedly kill his junior.
Pandya said she has sought a report on the incident from the district administration.