From the New York Times:
When the American filmmakers Jon Alpert and Matthew O’Neill traveled around Sichuan Province last year to document the anger of parents whose children had died in school collapses during the earthquake in May, they ran into a chilly reception from officials… Now, the Chinese government has denied both of them visas, blocking them from presenting their documentary, “China’s Unnatural Disaster: The Tears of Sichuan Province,” at the Beijing Independent Film Festival this week. The two men, who made the film for HBO with the co-producer Peter Kwong, said their visa applications were rejected late last week.
“We are extremely disappointed that the Chinese government denied our request for visas and that we will not be permitted to discuss this film with a Chinese audience in Beijing,” Mr. Alpert and Mr. O’Neill said in a joint e-mail message. “The denial of our visas fits in with a pattern of what seems to be a complete commitment on the part of this Chinese government to crush any inquiry into the possibility of wrongful deaths during the earthquake in Sichuan.”
…The Chinese government has gone to great lengths to silence any mention of the collapsed schools and, according to an official count, the 5,335 children who died or remain missing. In the weeks after the earthquake, which left nearly 87,000 people dead or missing, parents took to the streets to demand official investigations into why so many school buildings had collapsed even though other buildings around them remained standing. The parents said shoddy construction and corruption were the obvious causes.
An interview with the filmmakers on Democracy Now from May 2009:
See also this synopsis of the documentary on the HBO website.