Max Sidorov launched the campaign a month ago after seeing a YouTube video that showed four middle school students hurling insults at 68-year-old Karen Klein while riding the school bus.
A spokeswoman for Indiegogo, the fundraising website used in the campaign, says the tally has passed the $683,000 mark, with money pouring in from 85 countries.
That figure could still grow by the time the fundraiser ends at 11:59 p.m. PST tonight.
Four seventh graders in Greece, N.Y. have been suspended in the incident.
Sidorov, a nutritionist, has said he was motivated to act after being bullied as a child, and he hopes the grandmother of eight can use the money to retire early.
"I had some issues with bullying myself when I was a young kid and had just come to Canada, so I know where she's coming from," Sidorov said of Klein last month.
"Maybe we can send her on a great, early retirement."
-With files from The Associated PressSuggest a correction