“Investigators are examining midday meal samples and samples of victims’ vomit. Only the final report of inquiry will reveal the real cause,” Sinha said.
State chief minister Nitish Kumar has announced compensation of 200,000 rupees (Sh292,000) for bereaved families.
Free lunches are offered to impoverished students in state-run schools as part of government welfare measures in many of India’s 29 states.
Bihar is one of the country’s poorest and most densely-populated states.
Educators see the midday meal scheme as a way to increase school attendance. But children often suffer from food poisoning due to poor hygiene in kitchens and occasionally sub-standard food.
More than 130 students were taken to hospital in the western city of Pune last year after eating lunch at school, the Times of India reported.
A probe revealed that the food served to them was contaminated with E. coli bacteria, strains of which can cause food poisoning.
Food prices have soared in India over the last six years, causing increased hardship for the 455 million people estimated by the World Bank to live below the poverty line.