Final answer:
Researchers creating an experimental group and a control group through the random assignment of adolescents to different classroom setups are conducting a controlled experiment. The purpose is to measure the effect of the independent variable by comparing results between both groups, with random assignment enhancing research validity.
Step-by-step explanation:
When researchers randomly assigned adolescents to either a single-grade classroom or a mixed-age classroom, they were creating an experimental group and a control group. In this scenario, the experimental group would be the one exposed to the mixed-age classroom setting, which is the independent variable or experimental manipulation. The control group would be in the single-grade classroom and would not be exposed to the independent variable. The purpose of this controlled experiment is to isolate the effect of the independent variable on the measured outcomes, such as academic performance or social development, by comparing the results between the two groups.
The random assignment ensures that each participant has an equal chance of being placed in either the experimental or control group, thereby reducing the likelihood of bias and balancing out any other variables (lurking variables) that could affect the outcome. This method is a critical part of experimental design because it enhances the validity of the research. The difference in treatment between the groups should be the only significant difference to ensure that any changes in the dependent variable can be attributed to the experimental manipulation