A major challenge to promoting effective early science and engineering education is the lack of reliable and validated assessments that align with current educational guidelines for science and engineering. Existing early science and engineering assessments either cover a narrow range of concepts and practices and/or are not designed in a way to evaluate and provide information within theorized dimensions of science and engineering knowledge and skills. The goals of this study were to develop a preschool science and engineering assessment and to examine the factor structure of children's science and engineering knowledge and skills using the newly developed assessment. A 120-item assessment was developed and administered to 186 children (50.28% female) ages 3-to-5 years (M = 4.62 years, SD = 0.61 years). The overall best fitting structure of the assessment was found to be a three-dimensional model: disciplinary core ideas, science and engineering practices, and crosscutting concepts. Items that had low correlations with the overall test, loaded poorly onto their respective factors, or were found to provide overlapping information with other items (i.e., exhibited similar difficulties for the same content areas) were removed, resulting in a final and brief (48-item) version of the assessment. This study has important implications in that the newly developed science and engineering assessment can be used in both the research (e.g., evaluate curricula, interventions) and classroom (e.g., assess learning) settings to provide information at the dimension-level, and has the potential to transform how we view and instruct science and engineering during the early childhood years. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]