As he walked down a school corridor, a 13-year-old shouted out: "I hate you, you fucking queer".
But pupils who witnessed the abuse were "amazing", and told the boy he was "completely out of order", said Mr Parker.
"It was so heartening. That's what we are aiming for, to get pupils to decide for themselves what is acceptable," said Mr Parker.
Mr Parker, who teaches deaf pupils at College high school, a 1,000-pupil comprehensive serving three tough Birmingham council estates, came out to his pupils the day he started at the school four years ago.
He said he had been regularly verbally abused in his first year, but this was now rare partly thanks to the "100 per cent" support he got from colleagues.
He added: "When people start to recognise us as human beings, that's when we know we are making progress."