Monica, who is 8, describes herself as very good at math and science, but average in reading and art. She also says that she is good at basketball but a terrible baseball player. According to the neo-Piagetian view of self-concept development, Monica is using

Representational systems

Explanation:

Monica is making use of representational systems. People have a more highly values representational system in one thing than in others. From this they are able to create experiences. These systems are used more often than others and people are even able to perform more distinctly in that representational system than in others.

An example is Monica in this question who describes herself to be better in math and science compared to reading and art. And also better in basketball compared to baseball.