Astudent wants to determine how his classmates feel about school. he does a survey away from school so all participants will be willing to answer freely. in several cases, younger siblings of his classmates are present, so he lets them take the survey too. he surveys a total of 50 students. has he done a well-designed, controlled experiment?

I believe he has not. Firstly, his results aren't statistically significant. While I understand he can't survey hundreds, if not thousands of people, he could at least attempt his grade level, which ideally isn't humongous, and will be easy through the use of technology and social media direct messaging (to avoid peer influence)

Secondly, he did not account for peer influence. This is because by surveying a younger sibling while around their big sibling, they are more likely to adjust their answer accordingly. For example, if the little kid looks up to their sibling, they will want to be exactly like them, and attempt to imitate the answer. In contrast, if they don't like the elder sibling, or are in a rebellious phase, they are moer likely to choose the opposing answer that their sibling did, despite that they may hold the same view.