Not sure that I can offer any insight, but we see an identical pattern with our DD8.5. She CAN do math well... in her head, and when she is not bored. Put her in class with distractions, below-level work and a pencil in her hand and she does the same as you describes. She doesn't listen to or read instructions well, she rushes and makes mistakes on easy addition or subtraction. I am sure that her school thinks I am a lunatic. I keep saying that she knows much more, but until she 'shows' them what she knows I really don't think they believe me.
