In this study, we investigated Iranian high school students' preferences and beliefs about two types of form-focused instruction (FFI) for teaching and learning grammar, namely isolated FFI and integrated FFI. Using an adapted version of the questionnaire developed by Valeo and Spada (2016), we collected data from a large sample of senior high school students (n=1,058) in the Iranian public school system. The results of the analysis showed that most participants expressed preference toward having more integrated FFI grammar in their curricula. The analysis also indicated that learners' preferences for each of these types of grammar instructions vary depending on their high school major and length of exposure to English. The results are discussed with special attention to the context of the research and in light of the country's attempt to implement communicative language teaching at K-12 schools.