Final answer:
Jean Piaget's theory on the stages of cognitive development best explains the difficulties faced by middle school students in Mr. Young's project, as they may not yet be at the stage of abstract and systematic thinking needed to formulate hypotheses.
Step-by-step explanation:
To understand why Mr. Young's middle school students are having difficulty with a project related to scientific observations and hypothesis formation, Jean Piaget's theory on the stages of cognitive development is most applicable. According to Piaget, children's cognitive abilities develop through specific stages. As middle school students are likely in the concrete operational stage, which is typically from ages 7 to 11, they may not yet have fully developed the abilities associated with the formal operational stage (around age 12 and up), where abstract thinking and systematic planning begin to flourish. This might explain their challenge in creating hypotheses based on observations, as this task requires a level of abstract and hypothetical reasoning that may still be in development.