Hi underwhere,
I'd say the most important thing to remember in a piece like this is to give your two characters distinct voices. You've done a pretty good job at that, but you should feel free to ham it up a bit. After all, It's only a writing class.
Your narrator, Mom, can use time worn clinches, it's not often you get to do that so savor the opportunity. If one uses contractions, the other shouldn't. pick out a favored turn of phrase for each like starting a few sentences with "Of course," or "After all" don't overdo it but get a real feel for how each character talks, then be consistent and don't let the two characters overlap.
I thought the story was cute, kind of thought the mum was overly vulnerable and sensitive, but I like what you did and the ending was perfect IMHO

Yours
Mad Lews