Navneet, the 12-year-old student of St. Anthony Convent School, had consumed poison after returning from school on September 15.
He died at a city hospital late on Wednesday night after battling for life for six days, police said and informed that he had left a small suicide note behind in which he had written how his teacher Bhawna Rai treated him shabbily and gave him "extreme punishments".
In the pencil written note in English, the boy also said that some time back, another teacher Gopa had stripped him naked to punish him.
An official privy to the investigation into the matter said that they had cross-checked the handwriting of the deceased child with his school copies and it had matched.
Gorakhpur Superintendent of Police (City) Vinay Kumar Singh said that the class teacher named in the suicide note had been arrested and was being interrogated.
Other staff members and management of the school would also be questioned, if required, officials said.
Follow NDTV for latest election news and live coverage of assembly elections 2019 in Maharashtra and Haryana.
Subscribe to our YouTube channel, like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.