From a teacher's perspective (I am a 4th grade teacher), communication with the parent is key! I believe you should talk to your son's teacher a few weeks after school begins. Give your son and his new teacher a chance to know each other and the expectations of the classroom. As a parent, you should continue to have a positive attitude about school and about his teacher. When a parent has a negative attitude about school or the teacher, the child can pick up on it immediately, and have the same attitude. If after a few weeks you notice the boredom or behavior issue starting up again, discuss it with him. Have your son participate in the conference with his teacher so that he is able to hear what is being said. Therefore, he is aware of any consequences that will result in a negative behavior. He is also aware that parent and teacher are on the same team and are working together.
As far as being bored with the routine, he just needs to get used to having routines in his life. As a teacher, it is extremely difficult to rearrange schedules every single day. Students need stability in the classroom, and forming a solid routine is one of the ways to achieve success in the classroom. Otherwise, it would be utter chaos in the room.
Just remember that communication works both ways! Teachers don't always know what every student is thinking and feeling about certain issues. Good luck this school year, and let me know how he is doing : )