Considering the Research Findings Described in the Textbook, Which One

Considering the research findings described in the textbook, which one of the following is a true statement?

A) Most experts discourage teachers from having children tutor one another.
B) By the time children are eight or nine years old, most of them have developed effective ways of learning classroom material.
C) Students who see a classmate rewarded for doing something may engage in the same behaviour themselves.
D) Students are usually the best judges of what they do and do not know.