Bulli High School will remain closed for years 7 to 10 students on Thursday as clean-up and repairs continue after Monday night's severe storms damaged the school.
Classes will be held as normal for year 11 and 12 students.
A NSW Department of Education spokesman asked for patience from parents while repair works continued.
"Many services are working hard to clean and restore teaching spaces, staff rooms and the school canteen," he said.
Areas affected by the flooding include the administration building, maths rooms, industrial arts rooms, music rooms, special education classroom, the HSIE rooms, senior study room, the tiered learning centre, canteen and old gymnasium.
Students have been asked to bring their own recess and lunch food.
Staff will be on duty to supervise students from years 7 to 10 whose parents need to send their children to school.
Certain areas will be cordoned off to ensure the safety of students and staff.
The school's website will post details of when students can return to classes.
State Emergency Service crews responded to more than 437 calls for assistance in the Illawarra and South Coast since the devastating storms and flash flooding struck on Monday evening.
Acting deputy region controller Alex McFadden said that most of the jobs were centred on the Shellharbour and Wollongong city areas.
On Wednesday, the storm cell moved south, mainly affecting the Nowra region.
Ms McFadden said eight SES crews were mobilised.
Most of the jobs involved volunteers fixing leaking roofs and protecting properties at risk of flooding.
Ms McFadden said while rain was still expected to fall in coming days, the risk of flooding had decreased.
‘‘We do have rain continuing to fall and that is a risk to our communities but we don’t anticipate seeing the amount of rainfall we did in a short period of time again,’’ she said.
Ms McFadden warned residents to be wary of destabilised trees that may fall over due to the soaked earth.
- DOMINIC GEIGER