Researchers in various disciplines are interested in constructs that cannot be measured directly but are rather based on perception. In educational research, standardized questionnaires that ask for ratings are a common method used to capture person-related latent constructs, such as academic self-concept, motivation, or school anxiety. The same is true for instructional quality, which can be assessed by collecting ratings from students, teachers, or external observers. When comparing these alternatives, students’ perceptions show best predictive validity with reference to students’ school achievement and motivation (Clausen, 2002; Hattie, 2009). Furthermore, factor analyses illustrate that students’ perceptions can be used to distinguish meaningful dimensions of instructional quality (Lüdtke, Trautwein, Schnyder, & Niggli, 2007; Rakoczy, Klieme, Bürgermeister, & Harks, 2008). Indeed, this is evidence of structural validity and indicates construct validity. Studies have also shown higher reliabilities for students’ ratings in comparison to teachers’ or observers’ ratings (Clausen, 2002; Marsh, 2007). Thus, most scientists agree on the crucial role of students’ perceptions regarding instructional quality (Clausen, 2002; Ditton, 2002; Gruehn, 2000; Hattie, 2012; Hofer, 1981; Steltmann, 1992). Focusing on economic aspects, students’ ratings offer further basic advantages: (a) Students do not have to be paid for observing and rating. (b) In comparison to video-based observer ratings, students’ ratings require less material investment. (c) Inviting a colleague to observe and receive feedback requires more organization than obtaining feedback from students.