Non-formal learning settings like out-of-school labs provide students with insights into authentic learning situations. For example, in physics, students are engaged in experimenting as an authentic method. However, increasing the authenticity in experimentation can lead to overwhelming demands and hinder concept development and does not even need to be perceived as more authentic. We investigated the role of authenticity in experimenting in an out-of-school lab. Specifically, we explored (a) what influence the level of guidance has on students' perceived authenticity (RQ1), (b) which references students use in their assessment judging perceived authenticity (RQ2), and (c) to what extent perceived authenticity predicts students' learning outcomes (RQ3). To address these issues, a mixed methods study was carried out. One hundred forty-two students of seventh and eighth grade experimented in small groups and investigated the pattern that occurs when different apertures are placed between various light sources and a screen. Students were randomly assigned to one of two variants of the learning setting. In the guided experimentation group, students performed five pre-designed experiments and one freely chosen experiment, while the self-determined experimenting students freely designed all six experiments. A questionnaire was administered for perceived authenticity and interviews were conducted about the experimentation process. The learning outcome was measured with a pre- and post-test. We found no significant difference in perceived authenticity and learning outcomes of the two groups. To explain this, we conducted and analyzed interviews in terms of students' understandings of authentic research to determine the views their authenticity judgments were based on.