Can non-custodial parents whose children attend a private school/college get access to their children`s school reports?

Yes.

In most circumstances, it will be reasonable under the Privacy Act to allow non-custodial parents to have access.

There may be times when access will not be reasonable. A school will need to carefully consider these cases.

There is demonstrable risk to the child, including where a Court protection order is in place. The protection order may deny a parent access to a child, or limit the parent's access to information about the child.

NPP 2.1(a), the use and disclosure of personal information
The National Privacy Principles (NPPs) in the Privacy Act apply to private schools across Australia. They do not apply to State and Territory public schools, which are not regulated by the Privacy Act. Note the Information Privacy Principles apply to public schools in the ACT. Other privacy legislation may also apply to other State or Territory public schools.
10 Steps Guides to protecting personal information