A. Anxiety over performance on standardized tests often hinders a student s ability to master challenging new material.
---Ruling out, since there has been no mention of anxiety
B. A student's true intellectual development cannot be gauged by his score on a standardized competency test.
---The promotion gates seemed to be directed at elevating the students' basic skills and not just intellectual development.
C. The psychological damage a child suffers by repeating a grade outweighs the potential intellectual benefits of a second chance at learning.
---No mention of any damage to the child's mentality from repeating a grade.
D. Strict requirements for promotion do not lead to harder work and greater mastery of fundamentals among students fearful of being held back.
---Since there was no significant difference in scores during the second test among the promoted and repeated test takers so this suggests that the "promotion gates" are not rewarding enough for students to try and get higher scores.---So I feel this is the correct answer.
E. Socioeconomic factors as well as test scores influenced whether a given student in the study was promoted or forced to repeat a grade.
---Out of scope, no mention of any financial aid.