Which of the following studies meets the federal regulations' definition of research with human subjects?

The choice indicating a study of classrooms where time for reading is varied and assessments are collected meets the federal regulations' definition of research with human subjects because it involves obtaining data through assessments that directly relate to students, who are considered human subjects. In this case, the research not only impacts the students but also involves them directly as participants whose behaviors and performances are observed and recorded for analysis.

Federal regulations classify research with human subjects as any systematic investigation designed to develop or contribute to generalizable knowledge that involves obtaining data through intervention or interaction with individuals or identifiable private information. This definition encompasses studies involving direct interaction, such as assessments that can affect the participants' education and outcomes.

In contrast, the other options are less likely to meet this definition. Analyzing test scores without consent does not involve interaction with the students or obtaining their private information, which is a requirement for human subject research. Observing playground behavior may lack formal consent processes and the necessary engagement characteristic of qualifying research. Lastly, while interviews in a focus group setting might involve human subjects, they may not necessarily align with the educational context or assessment-related criteria described in the question as well as the selected option does.