Jean Piaget's theory on cognitive development is broken into four stages: Sensorimotor, Preoperational, Concrete, and Formal. Piaget's stages are divided by age groups, birth-2 years old, 2-4 years old, 7-11 years old, and 11-15 years old, respectively. So if a child is approximately 11-15, s/he would be entering the formal stage of cognitive development. The individual is at a stage of learning, or seeing, the world in a much more scientific or abstract way. S/he will begin to question and solve problems with more than one answer. S/he will be thinking more critically, trying to problem-solve.