when I was in HS, I didn't need motivation, but I knew people who did. It wasn't because they weren't smart, it was because they didn't want to put in the effort, or they had no interest in the classes and therefore didn't strive to do what they could (heck I even did that in one class). I think that offering incentive sets a goal and reward system, which is not necessarily a bad thing. Your parents obviously care about your performance in school and pay attention to what you are doing, which is an admirable quality you do not always see in parent these days. Put in the effort and make the goal, you'll feel good because YOU acheived something and got something to show you that your effort was acknowledged and appreciated. Then you can see that you can acheive and set a higher bar for the next time and prove to yourself that you can consistently acheive. Your dad should not waiver in the "prize" but should not chide you either, rather encouraging you to do better the next time, maybe compromising as previously suggested.
In my university FYI the marks go like this (some variation occurs between classes and profs):
A+=98%+=4.0
a=95-98=4.0
A-=92-95=3.7
b+=88-92=3.3
b=84-88=3.0 <- minimum requirement to continue in most degrees
b-=80-84=2.7
c+=75-80=2.3
c=68-75=2.0 <- minimum grade accepted
c-=63-65=1.7
d+=59-63=1.3<-scores around here put you on academic probation if consistent
d=55-59=1.0
d-=50-55=0.7
f=0-49=0
In my university FYI the marks go like this (some variation occurs between classes and profs):
A+=98%+=4.0
a=95-98=4.0
A-=92-95=3.7
b+=88-92=3.3
b=84-88=3.0 <- minimum requirement to continue in most degrees
b-=80-84=2.7
c+=75-80=2.3
c=68-75=2.0 <- minimum grade accepted
c-=63-65=1.7
d+=59-63=1.3<-scores around here put you on academic probation if consistent
d=55-59=1.0
d-=50-55=0.7
f=0-49=0
