RETRIEVAL PRACTICE Take a moment to answer each of these Learning Objective Questions (repeated here from within this section). Then click the 'show answer' button to check your answers. Research suggests that trying to answer these questions on your own will improve your long-term retention (McDaniel et al., 2009).

Cross-sectional studies (comparing people of different ages) and longitudinal studies (retesting the same group over a period of years) have shown that fluid intelligence declines in older adults, in part because neural processing slows. However, crystallized intelligence tends to increase.
     The stability of intelligence test scores increases with age. At age 4, scores fluctuate somewhat but begin to predict adolescent and adult scores. By early adolescence, scores are very stable and predictive.

At the low extreme are those with unusually low scores. An intelligence test score of or below 70 is one diagnostic criterion for the diagnosis of intellectual disability; other criteria are limited conceptual, social, and practical skills. One condition included in this category is Down syndrome, a developmental disorder caused by an extra copy of chromosome 21.
     People at the high-intelligence extreme tend to be healthy and well-adjusted, as well as unusually successful academically. Schools sometimes “track” such children, separating them from students with lower scores. Such programs can become self-fulfilling prophecies as both groups live up to—or down to—others’ perceptions and expectations.