Paul Vallas, superintendent of public schools for the city of Bridgeport in Connecticut, said he believed the boy took his stepfather's jacket to school on Monday without knowing the drugs were inside it.
"Children bring to school what they find at home," he said.
Police told the Connecticut Post the boy took 50 packets of heroin out of the jacket when it came time for a show-and-tell presentation, but Vallas said the boy only waved the heroin around at his cubicle. Police did not respond to messages seeking comment on Tuesday.
The boy's stepfather, Santos Roman, 35, went to the school and recovered the jacket, but police had already seized the drugs, officials said. Roman was arrested when he returned to the school, Vallas said.
Roman was arrested on suspicion of risking injury to a minor and drug charges. He appeared in Bridgeport superior court and was ordered held on $100,000 (£63,000) bail.
The department of children and families placed the boy in the custody of his grandmother, even though his mother went to the school to take him home, Vallas said.
Vallas praised the reactions of the teacher who initially noticed the drugs, worth about $500 on the street, and of others involved in the response.
