Willfull 6 year old boy, on my last straw

Ok...I need advice please, My wife and have been fostering 2 children (FS,3 & FD,2) since February. In late July, we were placed with their older brothers, which are twins (6 and not identical). We both new that the older boys would be a challenge considering their nick-names were hurricane and tornado.... We are having great difficulty with the older of the 2 twins. When school began, he was having issues staying in his seat on the bus. He was mis-behaving in school. Kicking and punching... in school or on the bus... Not listening to the teacher or any teacher for that matter. His brother did the same but with much work, we were able to corale him and he has improved immensly:clap: However, the older one doesnt seem to care. When we question him on his behavior he simply responds "Dad, I want my own way". I will give him this....He Honest! To try and give positive encouragement, my wife would meet them at the bus stop and issue little candies if they were good throughout the day. This worked for a little while. We made sure to praise them no matter how little the object of that praise was and we still do. But now, he just doesnt want to do anything. At least once a day, I get a call or a note from school noting his unwillingness to do his work. The bus ride is big now. He and his brother acted up on the bus and I received notice that one more infraction and he will be off the bus for 3 days. After that, its indefinite as to how long. What kills me is that his bus ride is only 12 minutes long. He is the first to be dropped off and the last to be picked up. :grr: This past Saturday, I walked with them the 5 miles to school to show them that the bus ride is the best and funnest way to go to school and that it would be a shame to have to walk. ( now mind you, I would NEVER make them walk to school, but I was hoping that it would deter them from acting up on the bus.....and for now, it has made an impact) What do you do with a 6 yr. old boy who wants his way?? My wife and I are out of ideas as to how to get him to change his mind. :grr: