Conventional data collection and analyses to evaluate opportunity to learn (OTL) is time and energy intensive. We propose an extension of an alternative approach suggested by Winfield (1993) by using a method to detect differential item functioning (DIF) to select items. These items are then used as initial indicators of possible difference in OTL in target schools. This study examines the feasibility of using the Mantel-Haenszel DIF method to detect different OTLs in rural and urban schools with data from the China Biology Olympiads Open Exam. DIF results are found to be associated with teachers' content coverage ratings and the theoretical item classification. It is concluded that the proposed method can be used as an initial step for OTL evaluation when the two types of schools are equivalent on aptitude, and the test items cover content area(s) with OTL problem. (Contains 5 tables.)