Smartphones as experimental tools (SETs) offer inspiring possibilities for science education, as their built-in sensors allow many different measurements, but until now, there has been little research that studies this approach. Due to current interest in their development, it seems necessary to provide empirical evidence about potential effects of SETs by a well-controlled study. For the present investigation, experiments were developed that use the smartphones' acceleration sensors to investigate an important topic of classical mechanics (pendulum). A quasi-experimental repeated-measurement design, consisting of an experimental group using SETs (smartphone group, SG, N[subscript SG] = 87) and a control group working with traditional experimental tools (CG, N[subscript CG] = 67), was used to study the effects on interest, curiosity, and learning achievement. Moreover, various control variables were taken into account. With multiple-regression analyses and ANCOVA, we found significantly higher levels of interest in the SG (small to medium effect size). Pupils that were less interested at the beginning of the study profited most from implementing SETs. Moreover, the SG showed higher levels of topic-specific curiosity (small effect size). No differences were found for learning achievement. This means that the often-supposed cognitive disadvantage of distracting learners with technological devices did not lead to reduced learning, whereas interest and curiosity were apparently fostered. Moreover, the study contributes evidence that could reduce potential concerns related to classroom use of smartphones and similar devices (increased cognitive load, mere novelty effect). In sum, the study presents encouraging results for the under-researched topic of SET use in science classrooms.