But the school's principal, Rex Allott, said Thomas had not been excluded from the camp, having been given the option to attend on a day-to-day basis - an option other parents had been happy to take, he said.
To soften the blow of not going to camp, Mrs Gestro took Thomas out of school for the three days so they could instead spend the time together doing fun activities.
But she received an email from the school telling her that in doing so he would be marked as "unjustifiably absent".
"I have no idea why.
"It's not like I was asking a huge thing from them. I think he should be given the chance to give it a go with his dad there for guidance," said Mrs Gestro.
"I also don't think he should be punished for a decision that the school has made. I don't see why he should be at school doing school work when his classmates are having fun."
She said she first raised the possibility of Thomas' father, a volunteer firefighter who lives in Wellington, accompanying him at an initial meeting about the school camp, which finished today.
"I was told they hadn't chosen the parents at that time.
"They couldn't confirm they would take him and told me to put in a form," Mrs Gestro said.
Consequently, Mr Bohanna was not chosen.
"They said not everyone's parents can go and I completely understand but there is a special circumstance to it. There is no leniency, no trying to get him there," she added.
Thomas was born with Ebsteins Anomaly, a congenital condition that effects one of the heart valves, limiting the amount of oxygen in the blood.
At 7, he had surgery to try and improve the function of his heart, however it was not as successful as hoped and he suffers from dizzy spells and fatigue when he over-exerts himself.
This year he has also suffered from "blue episodes" where his skins takes on an alarmingly grey tinge, for which he is undergoing tests at Starship Children's Hospital in Auckland.
Also diagnosed with Attention Deficit Hyperactivity Disorder (ADHD), Thomas' psychologist suggested he find other challenges to master this week in lieu of the camp activities.
One was going to the skate park to learn to do a tail whip on his scooter.
He told the Bay of Plenty Times he was "angry" and that he had been looking forward to the camp.
Another parent, who spoke on condition she was not named, said she experienced the same thing with her daughter, who also has a heart condition, two years ago.
"We put her dad's name forward and we were turned down. We had a meeting with them and they said they had all the parents they needed," she said.
"They were not interested in supporting us. They just don't have the understanding ... it's a hidden disability."
Both families were offered the option of taking their children to the Rotorua camp for day trips but they declined because of the inconvenience and wanting to give their children the full camp experience.
Mrs Gestro said while it was too late for Thomas, she hoped sharing his story would prevent the same thing from happening to other pupils in the future.
"I don't want it to happen to another child," she said.
Mr Allott said the school was "a very inclusive environment" and had a track record to prove it.
Thomas' father was one of 40 parents who the school had to turn down, as the camp could not accommodate all of them.
"The school has had to deal with some mixed messages around the needs of the child going to a school camp environment, revolving around medical issues and confidence of the child himself attending the camp," he said.
"The school has endeavoured to support the child to come to camp but the family has not taken that opportunity," he added.
While the school had made provision for Thomas to attend school while the camp was taking place there was "room for discussion" about him staying home during that time, Mr Allott said.
"We would look at the reasons," he said.