If one is involved in extra-curricular activities, one must gain consensus, work with people, motivate people, and work well with people. Cheerleaders must work together, editors of newspapers must meet deadlines and motivate people, club participants must learn to work with people of varying abilities and so on. Those who did none of this in high school and stayed home to study and study, got great grades, but never learned how to translate this ability into real-life working situations. They tend not to work well with people and are not creative intuitive thinkers. This inability tends to hinder them from realizing success in many of its forms.
Grades are also low on business employers list of requirements for an employee.
They need to learn how to deal with that in the real world. They need to be in an environment where they learn to deal with all kinds of kids of many races, backgrounds, religions. I also think that children benefit from learning how to deal with other kids who may make disparaging or negative comments to them, tease them, etc. It s part of real life to learn how to handle those situations. Home schooling doesn t seem to go beyond the loving scope of family and friends into the greater world with all its aspects.