This study aimed to: (a) understand practicing teachers' knowledge of model functions and modeling processes, (b) compare the similarities and differences between the knowledge of science and non-science major teachers, and (c) explore the possible reasons for the similarities and differences between the knowledge of these 2 groups. A 4-point Likert scale questionnaire was developed and used to measure the knowledge of 187 practicing elementary school teachers (94 science majors and 93 non-science majors) on model functions and modeling processes. The author selected 10 target teachers to conduct think-aloud interview and to explore their ranking. One month after completing the questionnaire, 28 volunteer teachers were selected for a follow-up interview to better understand the reasons for their responses. The results show that these teachers tend to agree or strongly agree with the items about model functions and modeling processes. The only significant difference between science and non-science majors was for the item "generating new ideas." Qualitative analyses of the follow-up interviews and think-aloud results showed that teacher education and professional development did not focus on understanding and using models. Science-major teachers tended to formulate their responses with reference to specific models, while the non-science major teachers' responses contained acquiescence bias. Finally, implications for science education are discussed.