The first stage of Piaget's theory of cognitive development is the sensorimotor stage. The sensorimotor stage begins when an individual is born and ends around the age of two (McLeod, 2015). Since the sensorimotor stage only lasts about two years, it is the shortest stage in Piaget's theory of cognitive development. According to Santrock in our textbook, “in the sensorimotor stage, infants construct an understanding of the world by coordinating sensory experiences (such as sight and hearing) with physical and motor actions” (Santrock, 2014, p. 95). Wood, Smith, and Grossniklaus state: “Infants at this stage cannot predict their reaction and therefore must constantly experiment and learn through trial and error. The concrete operational phase takes place approximately between seven and eleven years (Grossniklaus et al., 2001). . Saul McLeod states in an article that “the concrete operational stage marks the beginning of logical and operational thinking” (McLeod, 2010). It also explains how, during the concrete operational phase, “children acquire capacities for conservation (number, surface area, volume, orientation) and reversibility” (McLeod, 2010). According to Boeree, “conservation refers to the idea that a quantity remains the same despite changes in appearance” (Boeree, 2009). When children are in the concrete operational phase, they acquire the ability to put things in order based on a quantitative dimension (Santrock, 2014, p. 199). The ability to put things in order based on a quantitative dimension is known as seriation (Santrock, 2014, p. 199). McLeod states in an article: “their thinking is more organized and rational during the practical operation phase” (McLeod, 2010). In the article, McLeod also mentions that “during this stage, children can solve problems logically, but are generally not able to think abstractly or hypothetically” (McLeod, 2010). One of the last abilities that children usually acquire during the concrete operational phase is "the ability to classify or divide things into different sets or subsets and to consider their interrelationships" according to Santrock (Santrock,This stage is by far the longest stage of Piaget's learning). theory of cognitive development. It lasts from the age of eleven until adulthood (Grossniklaus et al., 2001). According to McLeod, “during the formal operational phase, adolescents acquire the ability to think abstractly” (McLeod, 2010). ). During this stage, adolescents are also able to merge and categorize things in more complicated ways (McLeod, 2010). “Adolescents further develop higher order reasoning skills” according to McLeod in an article (McLeod, 2010). As the article points out, “adolescents are able to perform mathematical calculations, think creatively, use abstract reasoning, and imagine the outcome of particular actions during the formal operational phase” ( McLeod, 2010). During the formal operational phase, “adolescents also become capable of systematically testing hypotheses,” says Atherton (Atherton, 2013). Atherton also states that “adolescents are concerned with hypothetical, future, and ideological issues during this stage” (Atherton, 2013). One of the last things adolescents acquire during the formal operational phase is the ability to modify their ideas without resorting to concrete manipulation (McLeod,