Ryan Coomber, 5, shown hugging his father, Robert, in a June 2009 photo, was bullied so severely that officials don't want him to ride the school bus anymore. (CBC)

A Saskatchewan father is considering suing the Prairie South School Division for failing to protect his son — who lost one of his legs in an accident — from being bullied on the school bus.

Robert Coomber's five-year-old son, Ryan, lost part of his left leg in a lawnmower accident two years ago. His left leg was amputated below the knee, and he wears a prosthetic limb.

Coomber said it breaks his heart to see Ryan being bullied after everything he's been through.

Ryan used to take the school bus from his home in Willow Bunch, Sask., to his junior kindergarten in Assiniboia, about 40 kilometres away.

But bullying and taunting on the bus have made that ride, which takes about half an hour on the bus, impossible.

"A lot of kids beat me up. Lots of big kids," Ryan said.

Kids on the bus have stolen Ryan's backpack, Coomber said, and one student tried to pull off his prosthetic leg.

Coomber spoke with the parents of the kids involved and thought the issue was resolved — until Ryan was punched by a 13-year-old on the bus on May 4, leaving him with a black eye.

"He was punched in the eye by one of the biggest kids on the bus," Ryan's dad said.

"He's young, he's five, he's disabled. I can't ride the bus and stand up for him, you know. He can't defend himself, so who easier to pick on than a kid who gets punched in the eye and sits quietly in the corner."

Coomber said he tried to speak with the teen's parents but got nowhere.

He then approached the bus driver and the school principal, who directed him to the Prairie South School Division.

"I asked for the child to be disciplined," he said. "I asked for him to be suspended from school [to] teach him a lesson because there's a zero tolerance for bullying.

"[But instead] we were told Ryan will no longer be on the bus, that it's not safe for him or my daughter and that we have to drive them the round trip."

Coomber said the school division even offered to pay for him to drive Ryan and his seven-year-old sister to and from school.

He said he finds the whole situation infuriating.

"It's just a shame that in his five years, [Ryan] has to be a victim over and over again."

The Coomber family is considering a lawsuit.

The Prairie South School Division told CBC News it would not comment on the matter.

Later on Tuesday, Saskatchewan's Education Minister said school bus operators are responsible for keeping buses safe.

"[Their] first responsibility is safety," Ken Krawetz told reporters at the provincial legislature in Regina. "Secondly, they have to be ensuring that behaviour on the bus is according to the rules that are put in place, and that's a difficult task."

Krawetz said the local school board was investigating the situation.