The thugs came after dark, as Do Viet Khoa and his family were getting ready for bed.
He says they punched him, kicked him, stole his camera and terrified his wife and children.
Khoa, a high school math and geography teacher, says the message was clear: Stop blowing the whistle on school corruption – or else.
For several years, Khoa has been fighting the petty bribery and cheating that plagues schools across Vietnam, where poorly paid teachers and administrators squeeze money out of even poorer parents.
Vietnam’s leaders approved a sweeping anti-corruption law in 2005, but implementation is uneven. The country still ranks poorly on global corruption surveys, and for ordinary Vietnamese, who treasure education, school corruption is perhaps the most infuriating of all.