Should I be concerned about my son's grades?

Just got my son teacher's email. She mentioned in her email that my son didnot understand how lower grades could affect him so my son never paid much attention to his work. In her view my son can be considered as "extremely smart" who never works. :(

My son is 8 year 3rd grader.

His grades distribution is as follows:

Half of the tests: VG (93-100%);
Half of the tests: S (85-100%).

His teacher complained the center of his life is : lunch, gym and recess and school work is never on the priority list.

Should I be really concerned? How should I help him to realize school is about study rather than play?

I start getting worried about him.