Editorial: A proposed new law would limit elementary school class sizes to a maximum of 20 students. Most parents support this measure and argue that making classes smaller allows teachers to devote more time to each student, with the result that students become more engaged in the learning process. However, researchers who the amount of time teachers spent individually with students, the students' average grades were unchanged.
What this question is testing
Your task
Find the assumption the argument requires in order for its conclusion to hold.
Common trap
Answers that would help the argument but aren't strictly required (sufficient, not necessary).
Winning move
Negate each choice — the right one breaks the argument when negated.
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