Concentration is a "sine qua non," a hallmark, of a Montessori Casa program. Yet, it happens that some children do not concentrate. They do not engage with the materials in the classic pattern of normalization. They are not challenged by ADD, ADHD, or a variant of sensory integration spectrum disorder. Instead of working alone, they prefer the company of others; they prefer to learn with others. One may wonder if their natural intelligence is interpersonal. Based on studies of brain development and findings from recent ethnographic research, this article describes a type of attention called "shared focus." Ethnographic research was conducted in Casa classrooms, located in four Montessori schools, during a 3-year period, beginning in 2008. The research involved observing classrooms and interviewing school staff, teachers, and children. "Children who do not concentrate" was a common concern raised by the teachers in those classrooms. A review of brain development research suggests concentration is a type of attention. Children may use a type of attention called shared focus when, for example, they laugh and run together on the playground, and when they leave their parents during morning arrival. Some children may also more naturally use this type of attention instead of concentration during the work period. (Contains 1 table.)