Final answer:
Fourth-grade students can typically line up by height because they are in Piaget's concrete operational stage, which allows them to think logically and understand concepts like conservation and seriation. Kindergarteners, being in the preoperational stage, may lack the ability to organize objects methodically according to specific attributes such as height.
Step-by-step explanation:
The cognitive concept that the fourth-grade students have that the kindergarten students lack is likely related to concrete operational thinking as described by the developmental psychologist Jean Piaget. Fourth-grade students, who typically fall within Piaget's concrete operational stage (ages 7-11 years), are capable of thinking logically about real situations and organizing objects in a methodical way, such as lining up according to height. This stage includes the understanding of conservation and the capacity to classify objects according to multiple attributes.
In contrast, four-year-old kindergarteners are still in the preoperational stage of development which occurs from ages 2 to about 7. During this stage, children's thinking is more self-centered and less complex, and they might not yet be capable of performing tasks that involve sorting or ordering objects according to size or other quantitative metrics consistently. They are still developing their abilities in understanding seriation which is the ability to sort objects or situations according to any characteristic, such as height.