Young children engage in pre-engineering thinking and play in their day-to-day activities. However, early childhood teachers often miss opportunities to facilitate and extend this type of play. In order to support teachers in this undertaking, the current study aimed to answer the question: What does pre-engineering thinking look like in preschool? Nine preschool classrooms were observed, and mixed-methods, multiple case study analyses were conducted with classroom observation data as well as teacher-reported data. Our findings indicate that children engage in engineering habits of mind throughout the classroom, children's access to materials and time to generate their own problems of interest are crucial, and teachers were often uninvolved when children demonstrated engineering habits of mind. Notably, teachers with > 5 years of teaching experience and lower teaching efficacy related to behavior management and engaging children in learning activities had classrooms with zero or few occurrences of engineering habits of mind. These results suggest that teachers may need support in engaging children in learning activities and managing classroom discipline before they undertake engineering-specific professional development. Topics to address in continuing professional development should focus on classroom environments, materials, and interactions that encourage children in generating and solving problems of their own interest as a way to facilitate pre-engineering thinking.