The incident started around 1:30 Tuesday afternoon at PS 20, 142-30 Barclay Avenue.
The kids drank what the fire department called "contaminated water" making them ill.
About 74 students were complaining about stomach aches after drinking out of water fountain, education officials said.
71 students were taken to an area hospital for evaluation.
Three others were treated at the school and sent home.
Officials speculated that the cause of the sickness could have been a backup of chemicals by an air conditioning contractor.
The school was notifying parents. The water supply to the school was shut off.
PS 20 will be open on Wednesday. The kids will get bottled water, officials said.