The objectives of this study were to develop a preschool science and engineering knowledge assessment and to examine the factor structure of children’s science and engineering knowledge using the newly developed assessment. Children’s science and engineering knowledge has been theorized to be made up of content-specific knowledge and the practices (i.e., inquiry processes) that give rise to this body of knowledge; therefore, it is hypothesized that a two-factor content knowledge and process solution will best depict preschooler’s science and engineering knowledge. Specific aims of the proposed study include: 1) develop an assessment that reflects the best and most current understanding of preschooler’s science and engineering knowledge and skills, 2) test the factor structure of science and engineering knowledge using the newly developed assessment, and 3) refine and evaluate the assessment using item response theory analysis and by examining convergent and discriminant validity with other science and literacy assessments. (author abstract)