Has anyone experienced agressive, hyperactive behaviors with their child or children?

My five year-old daughter is hyperactive and very agressive when she wants her way that has gotten her into trouble at school to where she is being checked for learning disabilities like ADD. I don't know if she has it or not, she might. She is the only child and her dad died almost three years ago and I am a single parent. She tries my patience in getting her way I know. I thought a lot of it she was wanting attention because I am the only parent. I know sometimes she can't stay focused and she is kind of spacey from what the teachers tell me, I think they are right. I worry about her because she is just starting out. We are going to a therapist that deals with children and getting her tested at school. I hope and pray something positive comes out of this for her. Any suggestions?