Final answer:
The dependent variable is the grades in reading in second grade, while the independent variable is attending head start.
Step-by-step explanation:
The dependent variable in this study is the grades in reading in second grade. This is the variable that is being measured or observed, and it is expected to change as a result of the independent variable. The independent variable in this study is attending head start. This is the variable that is manipulated or controlled by the researcher. By comparing the grades of at-risk children who attend head start with those who do not, the researcher can determine if attending head start has an impact on reading grades in second grade.