Few studies have explored school-level effectiveness and teachers' mathematics instruction within classrooms simultaneously. This study used multiple data sources, including classroom observations and teacher interviews, to understand the mathematical classroom learning environments, and teachers' perceptions and expectations about their students in effective and typical schools. Findings revealed that the overall intellectual quality of learning environments in mathematics gets differentiated by students' ability levels, favoring low-ability students when they were enrolled in effective schools. Our illustrative qualitative examples suggest teachers from effective schools tend to hold positive and high expectations of low-ability students, make accommodations, and adopt individualized instruction to meet their learning needs. Instead, the teacher from typical schools held a static perception of students' poor performance passing between generations.