The purpose of this study is twofold: (1) to develop and validate a three-tier diagnostic test on work, power, and energy (WPE) concepts and (2) to identify Turkish pre-service science teachers' conceptual understanding through this test. The Work, Power, and Energy Concept Test (WPECT) was developed through interviews, read-aloud sessions, and two pilot tests. Construct, content, and face validity of WPECT was achieved by various statistical procedures and expert opinions. The final version was administered to 709 pre-service science teachers (79.43% female, 20.57% male) from nine different universities which are located in seven official geographical regions of Turkey. The Cronbach alpha reliability coefficient of the test was estimated as 0.73. The analysis of the responses revealed that the majority of the participants showed an inadequate scientific understanding of WPE concepts. Four common alternative conceptions were held by more than 10% of the participants. These are as follows: (1) Constant pulleys produce a gain in energy and a corresponding gain in work; (2) The total amount of potential energy always transforms into the kinetic energy including frictional environments; (3) An object's total energy does not change when it is moved by a force; (4) A less muscular person moving the same object to the same distance at the same time delivers more power because s/he uses more energy. The results also presented that WPECT is a valid and reliable instrument to assess pre-service science teachers' alternative conceptions on WPE.