Base the grading system not on age, but ability to learn, and comprehend concepts

This petition proposes that the grade of a student be based on ability and not on age. That means that if a student can not comprehend, understand, or use the abilities taught in a specific grade (based on a test assumingly) that they will be put at a lower than average grade, with the same idea in place of putting people at a higher than average grade. Not every student is created equal in learning ability and willingness to learn. This system would make it so all children would be able to understand things at their own ability. This system is some what in place but I believe that it should be in place in a more extreme way.