According to erikson's theory, an elementary school-age child who does poorly in school, and does not get along well with classmates, is most likely to develop a sense of

I believe the answer is: Inferiority

According to erikson's every individuals have the need to have a sense of belonging/to be accepted by other members of the social group.
If they fail to achieve this, they would start to think that something is wrong with them and started to develop the feeling of inferiority.