I had a really big assignment due in for another course. .. due in.. a phrasal verb = due, required on time ...for another course. - the assignment is for a different course, not the one you were thinking of. ? I had (past tense) a really big (large) asignment (piece of work) ... due in ... (due, needed to be handed in soon) ... (the assignment is ) for another course. . Xd, why is your maths assignment late. I had a really big assignment ... due in .... for another course. I was working on that.

Hello, Xiodeng. "Due in for" sounds odd and wouldn't be used together. You would simply say, "I had a really big assignment due in another class." You could also say, "I had a really big assignment due for another class". I hope these suggestions help! If you are interested in taking English lessons, I am a professional teacher on Italki and am currently accepting new students. I would be happy to work with you.