Different people have different learning abilities. There are those who are very keen that learning does not seem to be a problem at all. They absorb what has been taught as a sponge and remember everything just like a recorder. These types of learners are easily bored because they do not have any difficulty learning at all.
The other set of learners are those who take so much time trying to understand and yet they still have so much difficulty despite the time allowance. They can range from non-thinkers to slow thinkers. While the non-thinkers are usually the lazy ones, the slow thinkers are those who would like to learn but just could not cope as fast.
They are merely different groups. Different approaches are used for each of the sets. The slow learners need more time and affection from teachers and parents. Understanding that their brains work differently will help in giving the attention needed. The slow learners are actually those who are more capable with the arts. They are visual. They imagine in images.
While you are blessed to have fast learner kids, you are also blessed with slow learners because you have more reason to spend more time to bond to help them get better grades.