Bachelor of Arts Dip Ed @ MQ consists of 4 years, in which you follow the prescribed course of teaching, and additional units as electives for your major in Arts. That is your focus subject. For Science, you can do the B Sci Dip Ed. and there is a B Com Dip Ed i think. But B Arts is for humanities based subjects of teaching that is, history, english, stuff like that.
There is also the Bachelor of Arts for 3 years with B Education (Secondary) Graduate course which i may be doing. Same concept plus the B Edu after you finish the BA after 3 years.