I can let grandparents to look after the kids for kindergarden, but not for primary school. Because when kids grow up, esp. in secondary, they will have their own friends and start to develop their own lifestyle. So, it is important to build up your relationship with the kids in primary stage.
If you miss out the chance, you may regret.
Yes, grandma can teach your kid well; some teachers can also teach your kid well but don't forget they are not kid's parents !
Your close relationship with the kid really needs spending time together, otherwise ... good luck to you.