I don't believe that grades determine intelligence because all grades are is just how well you memorize information and follow directions. A normal person who studies for 6 hours will always out perform a genius who doesn't study. If grades were truly a measure of intelligence a genius should always beat a normal person. As I said above grades are just memorizing information, thinking like every one else and effort. Plenty of intelligent people and successful people failed school. Edison was kicked out of school when he was 12 and Einstein didn't learn to read till he was 7. Both of these people are considered to be some of the greatest minds the world has ever seen but yet they both bad at school. Grades only capture a small portion of your life. Almost no teacher sees what you do outside of school and its not like you can blame them because they have their own lives too. School is designed to reward people who work hard at whatever they are teaching.

Another measure of intelligence is IQ tests and I don't think that these measure intelligence either. You can study for an IQ test by practicing analogies or number sequences and improve your score. If IQ tests did what they were supposed to you should be able to study for 30 mins and score 10 points higher. We limit peoples when we tell them that since they got a lower score than average they are stupid. An IQ test should just really be called a test on Matrix Reasoning, Spatial Recognition, Numerical Sequences, Analogies and Pattern Recognition.

In my opinion intelligence is ones ability to problem solve using logic and being able to think for themself. I dont think 1 test would be able to measure it for millions of people with accuracy. Intelligence is just something you have to figure to by yourself and we limit people when we tell them it can be measured in grades or IQ.