The male teacher admitted insulting the boy while speaking to a colleague in front of pupils.
He said the young boy “thinks he’s a bit of a gangster” in a classroom at Holyrood Secondary School in Glasgow.
But he denied a second claim that he said the boy was “over-confident for someone who was so overweight”.
Now the unnamed teacher has been “dealt with under the education department’s disciplinary procedures” after the boy’s family made a formal complaint to the school reported the Evening Times.
But the nature of the disciplinary action is unknown.
A spokeswoman for Glasgow City Council said: “The appropriate disciplinary action has been taken by the school following an investigation into the allegations made.
“There is no evidence that some of the alleged comments were made by the teacher in question and the family have been told this.”