Using intermediate grades to figure out which students to focus on is perfectly fine, and in fact I'm not sure it has much to do with what's being discussed. We're talking about a teacher being asked by a parent to create extra credit work so a student can jump from an A- to an A so they have better odds of getting into X/Y/Z.

I don't think anyone is suggesting that teachers can't dynamically adjust their attention across students as the class progresses based on grades. But at the same time teachers should not just be the pawns of parents. A parent shouldn't be able to just demand extra credit work for their child. This sort of special exception is something that should only be made by the teacher, at the teacher's complete discretion, if they legitimately think there's a truly good reason for treating that student differently.