Wollondilly Anglican College has submitted a planning proposal to accommodate soaring student enrolments.
The college is seeking to 'rezone land and facilitate future development and expansion' of the school.
By 2025 the school expects to have 1200 students enrolled, with its current enrolment at 900 students.
Wollondilly councillors unanimously supported the school's expansion plan, however they also raised concerns about potential traffic impact issues around the site.
Councillor Matthew Deeth said the college had been "a valuable asset to our community over the decades".
"I think that this is a great opportunity for expanding education within the shire," Cr Deeth said.
"I do note a couple of issues highlighted by the community particularly around traffic and the congestion that we find around the area when there are quite a number of cars coming through the one entrance.
"What this [proposal] does do is allows the college to put in a second entrance to ensure that we get much more streamlined management of the traffic around that area."
Cr Deeth said the council would also need to look at traffic solutions along the busy stretch of Remembrance Drive.
"I do think that council needs to have a much better look at improving road infrastructure around Remembrance Drive, particularly around the school," he said.
"It's certainly something that I have heard a lot of from parents at the college, that the traffic coming in and out of the school is quite a challenge.
"The school is doing their half and we need to look at what we can be doing to address the traffic challenges in that area."
Councillor Judith Hannan said community submissions had raised several issues which would need to be to addressed through the final approval process.
However, she said the expansion was a clear indication that school enrolments across the shire were growing.
"I do note that there are 900 students there and by 2025 they're expecting to have 1200," she said.
"I think that goes to the point of the fact that we were always told that we won't need another high school... we've had an expansion to Picton High School but Wollondilly Anglican College is still expanding even further.
"I think the fact that the college is expanding is very good, it's obviously got a good reputation and that's why students are travelling from far to go there."
The Wollondilly Anglican College Planning Proposal will now be submitted to the Department of Planning Industry and Environment (DPIE) for final approval.