Request for help from the UK

[jagash]

I am currently trying to write something up gaming-wise and would like to translate attribute scores to scores in schooling. I am quite certain that the North American system is far too different form the UK one though, so if anyone from across the pond could give me a little help? The descriptors and North American equivalents are as follows.

Crippled/Horrible/Failure, F
Poor, D
Satisfactory, C
Good, B
Excellent, A
Superhuman, (Would be beyond A)

Any help?