lil N
Hey Patty,
I will be straightforward and say that I did not work a single hour at a single job until Grade 12 external exams were over. That being said, it really depends on if you enjoy it or if you need the money or if the job is useful. Alongside my academics, I did a lot of extra-curriculars which required a large time commitment, including 2 bands, 2 choirs, sports, chess, competitions (one which I had to lead a team), volunteer tutoring etc. These all required me to be very organised throughout Grade 12.
I think the one advantage I had was because I didn't work, that gave me time for extra curriculars which gave me a really big advantage in uni offers, scholarships, resume, interviews (and in general conversation ๐). You've got a while but if you are thinking of applying for medicine, scholarships or other competitive degrees, then this would be something you want to consider. In applying for internships, placements, whatever it is, the idea is that: "the more you do, the more you get. The more you get, the more you do and its a endless cycle from there." To answer your question, if I had a part-time job on top of this, I would no way get the same ATAR; if I replaced all my extra-curriculars with a part-time job, I would probably get the same, if not better ATAR but I don't think I would get all the opportunities, awards and scholarships that I've received.
If you ask for my opinion, you have to understand that I will be honest with you so here goes: if you are planning on continuing with the part-time job, its vital for you to be very very organised. My advice is make a detailed timetable every term (you can experiment in Grade 10), finish your assignments early, stay on top of your content, revise consistently (to do well in exams) and cancel your shifts close to exams. If you plan on buffing your CV by doing extra-curriculars then I would recommend stepping down from part-time to casual (if you can) or just quitting work. A lot of my friends who got very high ATARs didn't work at all in Grade 12 (but did work before Grade 12). I was just an outlier that I didn't work at all but not to brag but I will admit that I topped all of them with the number of extra-curriculars and ATAR ๐.
What I would do is that, if I loved the job a lot, I would continue the job until the end of Grade 11 and then quit. However, that is my opinion and I don't know you best; only you know you best. Grade 10 and 11 are the times you trial and error and see what's best for you. If you're aiming for the very very top ATAR, you will find a way and you'll tell a different story to someone who asks this question from you.
TLDR: I think you can certainly get good grades with a part-time job but read above because there's more to it than that.
Hope this helps and feel free to ask more ๐.