A year ago today, armed terrorists seized a grammar school in the Russian city of Beslan. The documentary “Children of Beslan” (7 p.m., HBO) recalls the horrific event from the point of view of the young survivors.

Russians call Sept. 1 “Knowledge Day,” the traditional start of the school year. As video footage makes clear, the children of Beslan School No. 1 were dressed in traditional finery and accompanied by their parents and grandparents. Minutes into the school-day, the parents and children were taken hostage by Chechen terrorists armed with machine guns. They immediately herded everyone into the gymnasium and rigged the schools with bombs. After a three-day siege, Russian forces attacked. More than 350 people died in the resulting gunfire and explosions; half of them were children.

The young narrators recall nightmarish scenes with a chilling matter-of-factness. Several witnessed the violent deaths of their mother or father. A young boy describes being splattered with the brain matter of an exploding Chechen gunman. A girl remembers trying to reach an outdoor faucet during her harrowing escape from the school. Dashing through machinegun fire, she felt jealous of a group of her friends who were lining up to get a drink of water. But before she could reach the spigot, a Chechen fighter threw a grenade into the crowd of children, killing them all.

A powerful indictment of the inhumanity of terrorism, “Beslan” is disturbing to watch. Its young participants are clearly still in shock and emotionally scarred, probably for life. There’s something almost unbearable about watching a film consisting only of these traumatized witnesses.

“Beslan” also looks at the city in the aftermath of the attack, a sad place where the cemetery is continually filled with mourners, and where children aren’t children anymore.

Tonight’s other highlights

¢ Coverage of the U.S. Open tennis match (6 p.m., USA) continues.

¢ Tonight marks the last Thursday-night broadcast of “WWE SmackDown!” (7 p.m., UPN). The wrestling showcase moves to Fridays beginning Sept. 9.