"There is a massive hole in our lives - it feels like our hearts have been ripped out."
Taradale Primary is holding a private memorial service for Aryan at the school today.
Banerjee and his eldest son, Anshul, are guests of honour but Aryan's mother can't bear to go.
"They have made a 'buddy' bench with Aryan's name on it," said Banerjee.
"It's in the playground, which is appropriate. Aryan used to look out for little kids who looked lonely. He would go up to them and say, 'Are you okay?'"
Banerjee said the pain of losing Aryan, a popular pupil and promising footballer, was constant.
He coaches an under-12s football team at the school and said every time he walked past the window where his son was found hanging, "it hurts like hell".
Last year a report by WorkSafe - the national work health and safety regulator - ruled that Aryan's death could not have been reasonably predicted. No charges were laid.
But the Banerjees still have unanswered questions, which they hope will be addressed during the coroner's inquest in November.
They will be assisted by top lawyer Nigel Hampton, QC. He told the Herald there were many "inadequacies" in the WorkSafe report.
Banerjee said Hampton would be seeking "clarity about what happened, clarity about health and safety in schools and to ensure an incident like this doesn't ever happen again".
"[But] the reality is nothing will ever bring Aryan back. That's what we have to live with."
The Banerjees said it wasn't their son's fault he decided to climb out the window.
"He was a 9-year-old boy, who was trapped, panicked and didn't know better," Banerjee said.
Last weekend the family held a Hindu memorial service for Aryan.
"We did prayers invoking his spirit, asking God to look after him in whatever he's doing now."