Many factors influence teachers' thinking as they make decisions about curriculum, instruction, and content. Their own cultural background, cognitive style, and professional values and beliefs about education all subconsciously enter their daily decision making. Knowledge of students' needs and perceptions of students' abilities and backgrounds influence teacher judgments about “when" to teach “what" to “whom." The available resources for instruction-tests, materials, equipment, textbooks, time, and space-all have an impact on teachers' instructional planning.