How do i handle my daughter?

She is 11 and is failing two of her cles. she is SO forgetful. Finishes her homework but forgets to turn it in. Every answer she has for us is "i forgot" or "i don't know". had meeting w/teacher & she should be ping in all cles. is she wanting negative attention? she says no. We've punished & talked all we can to her about it. Could she have ADD? she's not hyperactive. We are trying so hard to help her...but what else can we do? She has no sense of urgency to improve...but she's a happy child.