Concentration describes the deep, sustained focus through which children achieve meaningful learning and optimal development. Dr. Montessori observed that when children engage in purposeful, freely-chosen work, they enter a state of deep concentration, during which they are able to refine their skills and cultivate discipline from within. This ability to concentrate is supported by the prepared environment, which minimizes distractions and provides enticing didactic materials that capture the child's interest and call to their powers of intrinsic motivation. As concentration is sustained, children experience a sense of fulfillment and self-mastery, which Hungarian psychologist Mihaly Csikszentmihalyi calls the "optimal experience" of flow.