Police Col. Pakdee Preechachon said Wednesday that 51-year-old Chonlathee Charoenchon, a Thai Muslim, was killed by gunmen at Ban Tanyong School in Bacho district in Narathiwat province.
He said four gunmen entered the elementary school's compound on two motorcycles, and one of them took the teacher's car after having shot him.
Attasit Rattanaklaew, the provincial education regulator, on Wednesday ordered closure of the school immediately after the incident. Other five schools in the district will also be closed indefinitely, starting Thursday.
A series of teachers' killings have triggered temporary suspension of classes in Thailand's Yala, Pattani and Narathiwat provinces, as local teachers demanded tightened safety measures for educators. The classes resumed after high-ranking government officials visited the area and promised to improve security for the personnel.
Teachers as well as security officials have been targeted as government representatives by the insurgents, whose apparent goal is a separate state from the predominantly Buddhist country.
Previous targeting of teachers had prompted state authorities to strengthen security measures and provide armed guards to escort the teachers to and from work, but not necessarily to supervise them during the course of the school day.
Nearly 160 school personnel have been killed since the Islamist insurgency first flared in Thailand's three southernmost provinces in 2004.
A total of more than 5,000 people have been killed in the Muslim-dominated sub-region.