Speaking to a television channel, a mother who had lost two children in the accident, said: "This is not an acceptable decision. The government officials should not be allowed to go free."
"Justice delayed is justice denied. We have been waiting for 10 years for the judgment. Freeing the 11 accused is not acceptable. The government officials should be punished...," said another parent.
The court held 10 people guilty and acquitted 11 others in the Kumbakonam school fire accident in Tamil Nadu that killed 94 children and left 18 injured in 2004.
The judgment comes a decade after the accident at the Sri Krishna Middle School July 16, 2004.
Among the acquitted are eight government and three school officials, while six school and four government officials have been held guilty.
The parents assembled at the court premises and urged the state government to go on appeal against those acquitted.