The modes of transportation to school for elementary school students have changed during the past forty years. Along with the significant decrease in walking and biking, passenger vehicle has become the dominant mode, which may induce traffic operation or safety problems around schools, and also impact trip generation rates/equations. The ITE Trip Generation provides trip generation rates/equations for Elementary School based on nationwide data since 1960s. Because of the possible inconsistency of old and new data, and the different character of Iowa with many other states, ITE rates/equations for Elementary School need calibrations for local use in Iowa. In this study, trip generation data were collected at twenty-three elementary schools in Iowa urbanized and suburbanized areas during school peak hours. Trip generation characteristics were analyzed for the schools built before 1980 and those after. Weighted average trip generation rates/equations in peak hours were calculated based on the number of students and the number of employees for older, newer and all schools. Multiple linear regression analyses were conducted based on several socio-economic factors possibly impacting trip generation at elementary schools. Since the results indicated significant differences between ITE rates and the calculated student-based rates, local student-based trip generation rates were recommended while ITE employee-based rates were still valid for local use in Iowa. Differences between older and newer schools were also proved in terms of student-based morning peak hour rate, transportation mode distribution and morning peak character. In addition, off-site drop-off/pick-up trips were found significant for older schools but not for newer schools in impacting traffic operation and safety status around schools as well as estimation of actual school zone activities.