Carson's Achievement in Fifth Grade Has Been Remarkable

Carson's achievement in fifth grade has been remarkable.Last year in fourth grade,he had occasional problems with distractions and difficulty understanding what was expected,but this year he has no such problems.Based on studies of factors related to student achievement,which of the following factors most likely makes the largest impact on Carson's success?

A) His teacher's content knowledge in fifth grade subjects
B) His teacher's knowledge and skill in classroom management
C) His increased interest in school
D) His increased ability to follow rules and procedures