The student demonstrated an adequate amount of effort to achieve an A-. Any "additional" effort should have been expended at that time. Alternately, the student can put that effort towards future assignments.
If the teacher wants to give out opportunities for extra credit (maybe because they feel the class is particularly challenging in general), they can do so. But students and parents are not entitled to extra credit, particularly those who already received a very respectable grade.
(I realize that for certain colleges, an A- isn't enough, but inflating everyone's grade doesn't help the situation.)