The provincial court Friday judged Nguyen Quang Chung, 49, guilty of raping and molesting the girls for over a year.
According to the indictment, Chung had many times asked the third-grade students to come into his office during break time at school, and raped them between 2015 and March 2016.
After the girls told their parents, a complaint was filed with the school board and a criminal probe launched by the police.
Chung taught ethics and was in charge of the school's Ho Chi Minh Young Pioneer Organization, a youth organization which is a part of all public primary and junior high schools in Vietnam.
Le Thi Thanh Thao, who was the school’s principal, told VnExpress that she had talked to the students and heard details of the abuse.
“One student said she was asked to clean his office room, another was asked to see him in the computer classroom... According to them, the abuse happened many times, and for a long time,” Thao said.
In Vietnam, more than 8,200 cases of child abuse came to light between 2011 and 2015, including 5,300 cases of sexual abuse, according to official figures.
In most cases the perpetrators were people having authority over the children, like teachers, school security guards and family members.