The present study investigated critical incidents in multilingual classrooms from teachers' perspectives to identify resources to make multilingual classrooms succeed. Our study is embedded in identity theories such as Mead's symbolic interactionism, translanguaging, and global language theory. The incidents referred to the language of instruction; a discrepancy between age, developmental stage and grade; an overlap between language skills in the language of instruction and disability; and parent contact. Traumas and frustration due to failure were reported by the teachers as playing a crucial role. The incidents showed two different paths. The first path presented incidents coming together with positive conditions, such as students' willingness to perform well, classmates' willingness to help, and consideration of students' language biographies; thus, the events turned to positive consequences for students. The negative path showed teachers' perceptions that students in monolingual classrooms were frustrated, excluded, and did not perform well when no positive conditions existed. Implications for different actors were outlined.