I believe even if attachment plays a large role in determining the well being of a child's future life, there are too many confounding variables for such a claim to be true. How well a child will perform really depends on his experiences. Therefore, any bad influences, such as a violent family, friend bullies, smoking parents, etc, could have dragged down on how well the child develops. On the other hand, if the child is sent to a good school and always receives a lot of attention from his parents, he may develop better. So these my alternative suggestions of how a child's development may be influenced.
I'm not sure exactly what claim you are disproving. If it is the claim that attachment style is the only determinant of the quality of later life, then you may be throwing the baby out with the bathwater. Attachment style can be one of many factors. Just because a child is influenced by other things doesn't mean that attachment style is irrelevant.
I understand what you are saying and I definitely agree. In childhood (meaning up to age 18), a person spends a lot more time in school/social settings than in the home. Thus, no matter how caring the parents are, if the person is constantly faced with bad situations outside of the home, the person will definitely be affected negatively. School bully and negative experiences are great examples that you mentioned.
