Your child is slowly transitioning, but still not very matured to handle conflicts and be expressive about the same. Besides playground, the ride to school and back home in the bus is another place where bullying can occur. Making matters worse is bullying in the bus goes unchecked and can make the child feel trapped and helpless. You may also observe him resisting to go to school by bus daily. He may either be bullied or is a witness to bullying. You have to do all that to ensure your child is safe.
What you need to do
Once he is back from school, make it a habit to ask him "How was ride to school and back home. Anything that he would like to share with his Mom". Take time to really listen. If he tells about the bullying behavior, take corrective action. Either you can contact the parents of the bully or the school administration(transport division).
Tell him regularly that no bullying has to be tolerated. If complaints are coming from many children about the bullying behavior of one child, as a group of parents you can talk to the parent of the bully. A note in the school almanac can also be sent to the class teacher. Equally important is teaching your child to speak up when he is a witness to bullying on the school bus. Bullying can affect the child physically, emotionally, verbally or socially on a daily basis. Hence, its important to build trust, communicate and listen to any of your child’s concerns.