This quasi-experimental study adds to the small existing literature on orthographic-related teacher knowledge in an English as a foreign language (EFL) context. The study examined the impact of a course on English orthography on predominantly non-native-speaking EFL preservice and inservice teachers' orthographic content knowledge, and the extent to which these teachers retained orthographic-related content knowledge four months after participating in a semester course on the topic. In addition, the study examined the relationship between participants' acquired orthographic-related content knowledge and EFL spelling. Both groups of teachers that studied in the course improved on overall orthographic-related content knowledge, both immediately following the course and longitudinally. Preservice and inservice participants showed similar levels of orthographic knowledge prior to course participation and both showed significant improvements compared to controls following course participation. Participants also retained knowledge four months after course completion. Overall, the inservice teachers scored higher on orthographic-related knowledge, possibly as a result of the immediate application of their newly acquired knowledge. An unexpected finding was a lack of interaction between acquired orthographic-related content knowledge and pseudo word spelling scores. Possible methodological limitations, such as number of participants as well as the length and scope of the course, may explain this outcome. This paper also discusses practical implications of this study for EFL decoding and spelling instruction.