The staged opening of schools was to begin on October 25 starting with year 12, kindergarten and year 1.
But on Wednesday evening the cabinet agreed that school returns would start on October 18 for this group, with the official announcement expected on Thursday.
All other students will be integrated back onto school grounds over the following two weeks, on October 25 and November 1.
It comes after NSW exceeded vaccination double dosage expectations, and as the state is set to reach 70 per cent full coverage ahead of schedule.
Parents of young children who need to leave home for work on October 11 - when the state begins opening up - will no longer be able to supervise learning.
The Independent Education Union says it is deeply concerned by the lack of consultation and believes the former staged plan was the safest option.
IEUA acting secretary Carol Matthews told AAP they had still not been contacted regarding the latest decision and there was a lot of "nervousness" given how contagious the Delta variant is.
"I don't think people will be ready for those dates to be adjusted," she said.
"There are no government guidelines in place about ventilation and air filtration in schools," Ms Matthews said in a statement.
"NSW non-government schools are only just starting to take steps in this area."
Following months of disrupted learning, Labor is calling for the COVID intensive learning program to continue into 2022.
It says the extra tuition should also focus on western Sydney areas hardest hit by restrictions.
Labor also wants the government to fast-track additional school counsellors to support students' mental health after months of lockdown.
"We know the heavy toll lockdowns have placed on children, particularly those in western Sydney and southwest Sydney who have spent the longest in lockdown," deputy Labor leader Prue Car said.
"The NSW government needs to extend support to our schools to help get students back on track and ensure the lockdowns don't leave any students disadvantaged."