As a teacher, children are not held over because of outburst it's suppose to be in regard to her academics. Now that she is being physically aggressive you should ask to speak to the social worker or guidance counselor and ask for an evaluation to see if she needs to be placed in a smaller classroom setting. Sometimes as a parent, you try to protect your child from being labelled "special ed" but sometimes in the long run a small classroom setting is what she may need. She's been through kindergarten before and know she is the "older" child so she appears to be much bigger than the other children. Parents are often overwhelmed when they're child is the aggressor and may feel that the entire school staff is against their child. The school is only looking out for what's best for your child as well as the other children. Next time you speak with the principal have a open and willing mind to listen for suggestions which could be tutoring, counseling, homework, rewards and consequences. All behavior is learned and can be adjusted. At 6 years old her behavior can be corrected and redirected. Hope I helped.