A school district wants to determine whether offering a new study-skills workshop causes tenth-grade students to submit more assignments on time. The district randomly selected 12 of its 36 high schools. At each selected school, researchers randomly selected 80 tenth-grade students to track for one semester.
Before the semester began, each selected school's principal decided whether to offer the workshop based on whether the school's schedule could accommodate it. Five schools offered the workshop, and seven did not. At the end of the semester, students at schools offering the workshop submitted, on average, 9 percentage points more assignments on time than students at the other selected schools.
Which change to the study would most directly enable the district to support a causal conclusion about the effect of offering the workshop for tenth-grade students at the selected schools?
For a study-design question asking how to establish causation, focus first on how the treatment groups are created. Random assignment is the key feature because it helps prevent preexisting group differences from providing another explanation for the observed outcome difference. Do not choose an option merely because it increases the sample size, adds more observations, or collects more background information.
Hints
Focus on how the groups are formed
Consider whether the schools that offer the workshop are made comparable to the schools that do not offer it.
Distinguish more data from a stronger design
A larger sample, additional observations, or more information about principals' decisions does not necessarily eliminate preexisting differences between groups.
Look for random assignment
For a cause-and-effect conclusion, identify the choice that changes how schools are placed into the workshop and no-workshop groups.
Desmos Guide
Use study-design reasoning instead of Desmos
Desmos is not needed for this question. The relevant issue is whether the study uses random assignment to create comparable workshop and no-workshop groups; no graph or calculation can replace that design feature.
Step-by-step Explanation
Identify the limitation of the original design
In the original study, principals decided whether their schools offered the workshop. A school's ability to accommodate the workshop could be related to other factors, such as scheduling resources or existing academic-support programs, that also affect assignment submission.
Identify the needed design feature
To support a causal conclusion, the schools should be randomly assigned to the workshop condition or the no-workshop condition. Random assignment makes preexisting differences between the groups less likely to explain a difference in outcomes.
Evaluate the proposed changes
Randomly assigning five selected schools to offer the workshop and seven not to offer it directly addresses the original study's confounding problem. The other changes may provide more data or background information, but they do not randomly determine which schools offer the workshop.