Ah ok - the Junior School makes sense, I think I have heard that too, along with a Junior School campus at a High School - like Mt Waverley Secondary for eg. who have a Junior/Middle and Senior school campus I think.

As for enrolling, it really depends on the school. Some schools that want enrolments will take students from wherever they are from, others are full to capacity so it isn't so much that they are zoned like the Secondary schools but they do prioritise based on who lives closest I think and it might be a first in first served. Which area of Melbourne are you looking to move to? I would be calling the public schools you are interested in once you move to find out what their process might be.