Sandra wants to study how students in their senior year of high school prepare for college. She starts by visiting an elite boarding school nearby. Sandra knows that to make general claims about seniors preparing for college, she will need to:
visit more schools so that her sample is representative of the group she wants to generalize to T/F

That statement is true

Explanation:

In research,  generalization occurs when we make a statement that applicable to a certain group or sitaution.

In the example above, Sandra wants to study study how students in their senior year of high school prepare for college.  This means that the group that she wants to generalize are the students in the senior year of their high school.

If Sandra only visit the elite boarding school and use it as her only subject, the result wouldn't represent the students in senior high school as a whole.  The students in elite high school are more likely to be well-off and have better learning system compared to the students in average high school.

This is why Sandra needs to visit more schools with different criteria in order to make general claims about the seniors.