Melissa and David de Jong want to send four-year-old Jonah to the same school as his sister Alianna, but are worried he won't be accepted under a revised enrolment policy.
The NSW Department of Education's crackdown on out-of-area enrolments means Yass Public will be the designated school for families living in north Yass.
On the south side of town, families will be directed to Berinba Public.
Mr and Mrs de Jong live in the catchment area for Yass Public, where Alianna is enrolled, but will move into Berinba Public's catchment area early next year.
"I had heard a rumour that siblings would be able to follow," Mrs de Jong said. "If this is not the case, then I'll be really upset because, with Jonah's special needs, he needs his big sister to look out for him.
"I would really hate to change Alianna's school as she has already settled in and we really like it there."
The Enrolment of Students in NSW Government Schools policy was updated on August 14 and applies to new enrolments from 2020.
Under the policy, each school is given a strict cap on the number of non-local enrolments it can accept.
Out-of-area applications for siblings of current students will still get priority, but only if the school hasn't reached its cap.
Schools in Yass are close to reaching capacity, a spokesperson for the Department of Education said.
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"Across the state, many communities are changing. Some schools that used to be able to accept out-of-area enrolments no longer have the room to do so," the spokesperson said.
The policy was revised to ensure every student had a place at their local school, the spokesperson said.
Small schools such as Bowning Public are set to benefit from additional enrolments, with areas such as Good Hope Road falling into its catchment area.
However, for families, that means travelling through Yass, past the town's two public schools and onto the highway to get to Bowning.
A parent who lives on Good Hope Road said she was told the zoning had been determined 'as the crow flies' rather than by access roads.
The other option for families will be the town's Catholic school, Mount Carmel.
Yass Public School principal Michelle Fahey said her school was very close to its enrolment cap.
She said the principals in the Binit Binit Learning Community had discussed the policy and were on the same page.
The Learning Community includes Yass Public, Yass High, Berinba Public, Binalong Public, Bowning Public, Gunning Public, Wee Jasper Public, Jugiong Public, Rye Park Public, Dalton Public and Boorowa Central schools.
Students currently enrolled in NSW public schools will not be affected.
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