The emergence of learning objects for teachers as a focus of educational concentration is relatively new and much of the discussion has not been based on the actual development of objects, but different definitions, learning theories, properties and standards or decorative packages of learning objects (LOs). Also, in many teacher education programs, prospective teachers take a computer literacy class separate from content methods classes and rarely engage in producing authentic teaching/learning experiences. This research goes somewhat to address prospective K-12 teachers’ development of learning objects. In this study, a group of prospective K-12 science teachers’ learning objects were examined, evaluated and compared with LOs developed by instructional designers (IDs). A total of forty learning objects were closely investigated and effectiveness of eight of them was tried out with 180 target students in classrooms. Detailed analysis of the LOs demonstrated that while both the preservicers and the IDs use similar number of instructional elements in their LOs, the IDs seem to represent concepts and procedures with screen objects other than the text and used the text for supporting graphical objects. Both groups developed LOs similar in quality measured with the LORI 1.5. Statistical tests on the data obtained from classroom usage of the LOs showed marked improvements in the students’ learning.