I'm in Vic I've only ever heard the term "junior school" used to refer to P-6 section of a P-12 school

My son goes to one and the junior school is up to and includes year 6

Kindergarten and preschool are used interchangeably in Vic and neither is compulsory

Form 1 = Year 7 but I have not heard the year levels referred to as 'Form..' in a very long time