John Boydston wrote:

In one of the later mangas, there are hints that Akane is at least the
equivalent of a "B" student (an 86 on a test). Ranma's test score is never
revealed and as far as I know there is no actual evidence as to his grades.

I'm not sure, but didn't Hinako once call Akane her best student? 
Seeing how strict Hinako is, that means Akane probably does have very
good grades.

The problem with the cliche, as with all cliches, is that the cliche does
not take into account the irregularities in Ranma's training. Several people
like to portray Ranma as unintelligent (witness Lord Archive's page where he
claims Ranma's IQ is about 95). Unfortunately, there is a lot in the manga
to contradict this. Here are some of them:

Learning the Umi-sen-ken after being shown it, once.
Realizing what Rouge's power source was and helping her achieve full power
without it.
Rapidly coming up with countermoves to techniques he has just had used on
him.

There are others. My contention is that of several other writers. He is not
unintelligent; he is uneducated.

Yeah, and that doesn't refute the 96 IQ theory.  To clarify: if Ranma
were to take an IQ test, he would probably score poorly.  Why?  Because
IQ tests are based largely on education; they assume that the taker of
the test has been to school on a regular basis for their age. 
Naturally, it isn't much of a leap of logic to say that Ranma has NOT
had regular schooling for someone his age.  I wouldn't be surprised if
you could count the number of years he's been in school on one hand.
This simply shows a weakness of IQ tests.  While I wouldn't call Ranma a
genius, his IQ would probably be misleading as a measure of his actual
intelligence.