Wesley Walker, 14, of Longton, Stoke-on-Trent was set the homework as part of his creative writing lessons.
His letter made references to his own funeral, and how he would be with his deceased nan and grandad. He gave the note to his mum as he went up to bed. His mother, Vicki, then read it, and was terrified her son was going to take his own life.
"I felt I was going to find him hanging from his bed, I found it sick," she said.
Wesley's school, the Discovery Academy has apologised for causing any "distress".
Headteacher Rob Ridout said: "It was never the intention of the exercise to cause distress, in fact it was the total opposite of that. We apologise for what happened."
"It's unfortunate that the context of this exercise wasn't explained to Wesley's parents."
Wesley interpreted his homework to be a letter written as though he had a terminal illness and only a few hours left to live.
He wrote: "I want you to remember the fun times and the happy times, at my funeral make everyone were [sic] bright colours to remember my personality.
"I know I have been a pain at the best of times but I'm with Nan and Grandad now so I love you and goodbye."
The youngster ended his assignment by writing: "Please be strong for me" and signed off with six kisses and a heart.
He said it felt 'normal' to write 'because it was a lesson where we do creative writing.'
His shocked mum said she was convinced he was about to take his own life and that 'maybe he felt he couldn't take any more.'
"I spoke to him and he said it was something they were asked to do at school, I felt it to be really sick.
"I just don't think schools should be asking children to write things like this especially when it can be seen as a suicide note, I don't agree with it."
Mr Ridout explained that the exercise was part of an 'expressive art' lesson.
He confirmed Wesley showed the letter to a teacher and that he was told to take the letter home, adding: "The exercise was to enable young people to express emotions and share things with loved ones that they never normally say.
"They were asked to imagine what they would say if they had a short time left and many pupils and their families found it an encouraging and positive experience.
"It's unfortunate that the context of this exercise wasn't explained to Wesley's parents, and we'll look at the way exercises like this are communicated to our students in the future."
That poor mum! How upset must she have been? Do you think schools should be setting this sort of thing for homework?