Objectives 
This study tests whether juveniles’ responses on sensitive topics such as self-reported delinquency, victimization, and substance use are comparable when teachers versus external persons supervise students while filling out online questionnaires.
Methods 
Eighty classes with 1,197 students (9th grade) in eastern Switzerland were randomly assigned (at the class level) to supervision either by their teacher or by an external person (i.e., researcher). Students filled out online questionnaires about self-reported delinquency, victimization, and substance use in the classroom while being supervised either by their teacher or by an external person. Prevalence rates were compared using Chi-square tests.
Results 
Only three out of 57 comparisons show significantly different outcomes. Whenever differences are found, and contrary to our expectation, sensitive experiences are more often admitted when students are supervised by their teacher. Effect sizes do not exceed 0.6, and are thus all below the limit of a small effect.
Conclusions 
Using online questionnaires with teachers as supervisors may not affect validity while making surveys less expensive and intrusive.