The body of 15-year-old Noppakao Sita was discovered in a swamp near the school on Tuesday.
Investigators believe he was forced to jump into the swamp even though he did not know how to swim as part of activities organised by the Ban Na Kor Wittayakom School.
On Wednesday, the boy’s parents and school friends plus representatives of the school were summoned by police for interrogation.
Noppakao’s friends told police the activity featured wargames, in which students had to jump into the swamp to avoid “bombs” – stones aimed at them by their teachers. No life jackets or rubber boats were provided for them for safety, while students said teachers did not indicate which parts of the swamp were deep or shallow.
On Saturday, Buachuen Sita, 48, and the boy’s stepfather filed a complaint against the teachers at the Huai Mek Police Station.
Some teachers were also charged with violating the Alcohol Beverage Control Act as they had been drinking during the boy scout activity.
Police said several staff members and the director had been summoned for interrogation, but most of them postponed the meeting.