Jen-I am sorry to hear that your daughter is having such a rough time in school. I too raised a child with ADD and he was not diagnosed until 8th grade. By then, not only had his grades suffered, but so had his self-esteem and interactions with others. School and homework were a constant battle. And I suffered from horrible "mother guilt".
I know that it is difficult for you to have to put your child on meds at an early age, but remember how much better you did in school and how it will help her too. Once you find the right medicine for her she will feel so much better--will be able to concentrate and complete tasks in a timely manner---thus raising her grades AND self esteem. If she had a physical illness that required antibiotics or insulin, for example, you would not hesitate to give her the medicine she needs. Do not feel guilty about doing what is best for her in this circumstance too.
I have no experience with Concerta, but your doctor should be able to provide you with literature and answer any questions you have concerning it. The Internet is also a great place for reading more about ADD and its treatments. I hope it works out for you and your daughter.