The ambush which took place in Yala province was similar to the killing of 12 soldiers on May 31, the single deadliest attack on security forces in three years of violence.
Muslim and Buddhist teachers are increasingly the target of attacks in Thailand's south because, officials say, they are seen as tools of the state, and they are easy targets.
Friday's bomb blast follows a series of arson attacks on schools across the region earlier this week.
Dozens of schools have been gutted by arson 
across Thailand's south [GALLO/GETTY]
So far more than 260 schools in the region have been closed because of fears that security forces cannot guarantee the safety of children or teachers, despite armed escorts.
In a separate attack elsewhere in Yala province on friday, five Muslim men were injured when gunmen sprayed bullets into a village teashop.
More than 2,200 people have been killed and thousands more wounded in separatist violence that erupted in the south in January 2004.
Thailand's three southern-most provinces were once an autonomous sultanate, until the Muslim-majority region was annexed by mainly Buddhist Thailand a century ago.
The Thai military currently deploys some 30,000 troops in the provinces in a bid to stem the ongoing violence.