The kids were part of a 63-student group on a trip from Surat Thani and were headed back home on Friday before the incident.
All of the students, many of them 13-year-olds, were taken to the hospital after losing consciousness. Screams from the students woke up the entire camp after the group had fallen asleep on Nai Yang Beach.
Police questioned their teacher, Mrs Jaree Noiprom, 45, who said the students were hysterical.
All but three of the students, two 13-year-olds and a 14-year-old – all girls – regained consciousness within hours. When they awoke, the students did not know what had happened, police said.