I translated "On Saturday we eat chicken" as "Sabato mangiamo pollo", but it was marked wrong because I didn't use the article - il sabato. I haven't seen articles used with days of the week anywhere else; could someone explain why the article is necessary here?

with days of the week it is used to indicate something that recurs on the same day--a habitual action. The meaning is that on each Saturday we eat chicken, as opposed to something that just happens on one Saturday.

i also am wondering why "su sabato mangiamo pollo" is incorrect.

When exactly do you use "lo" instead of "il/la"? I thought you replaced "il/la" with "lo" when the noun being described begins with "z" or "s". "Sabato" begins with an "s" but its definite article is "il", not "lo"...?

I wrote "A sabato mangiamo pollo" and it marked me wrong. This is getting a little annoying.

Why is it wrong for putting 'A sabato'?

Can this also be (Su sabato mangiamo pollo

I believe 'a sabato mangiamo pollo' is also correct, although it was marked as incorrect