Well there isn't really an exact definition for intelligence however the Intelligence Quotient is quite close.

I agree, however, that people who may do well in school may not excel on IQ tests and the same vice versa. In my opinion, just because someone is able to remember and understand concepts (basically being able to regurgitate information) does not show someone's overall intelligence. A huge aspect of someone's intelligence is the creation of new ideas and concepts. Public schooling in general does not encourage this type of creativity.

Anyway, apart from the diagnosis of MR and neato statistics which confirm common sense (such as higher crime rate the lower your IQ), I think IQ does not serve much of a purpose. The tests are extremely subjective and they have an extreme amount of variability.

Just my thoughts.