Not at all. A student can be very smart, but if the teaching style does not suit their learning style then the student could fail to show his/her true performance capabilities.

But school is about informing the student and the grades are just there to show that the student has learned the material.

No. The grading system says that an A in math is equivalent to an A in PE. So, there is something wrong. I don't really have an idea how to fix it right now.

Test like the SAT and ACT are best for this. You can teach yourself all of the material in a way that suits you and then take those test. Then your grades in school don't even matter.

Definitely not. If a school is supposed to be a place of learning, then the emphasis should be on learning, not on pressure to have learned all of the material prior to the first class.

Rather than measuring and permanently recording a student's flat performance, what should be measured is a student's improvement throughout a course. If not, students will find themselves with failing marks from classes they learned a lot from and only passing classes where they knew all of the material beforehand.

The grading system only measures if a student can remember facts, not if they can learn AND apply what they learned to real world situations and different events that occur. It's good to remember that "Columbus sailed the ocean blue in 1492" (I think that's right haha), but knowing how to critically think is a skill no one can actually teach or any modern grading system can accurately measure.