and engage in other complex symbolic activities involved in oral language, reading, writing, mathematics, and social behavior is dependent on the development of attention, memory, and executive function (Lyon, 1996). Difficulties with these more cognitive aspects of self-regulation can lead to problems in school, in relationships, and in life.

Self-regulation of attention and cognitive abilities is often described as a form of executive function. Executive function is an umbrella term used to refer to a variety of interdependent skills that are necessary for purposeful, goal-directed activity, such as learning to hold a crayon and scribble on paper, string beads, or hand a cup of juice to a friend without spilling (e.g., Luria, 1966; Shallice, 1982). To engage in these sorts of behaviors, the child must be able to deploy a series of relatively complex skills. They include generating and maintaining an appropriate mental representation that guides goal attainment (“I need to hold up the string and put the end through the hole in the bead”), monitoring the flow of information about one's progress (“I've got one on, now I'll try another”), and modifying and flexibly adapting problem-solving strategies so that behavior is continually directed toward the goal (“Oops, that bead was too hard to string; maybe I need to find a bead with a bigger hole”). These skills are needed whether the task involves correctly sorting colored blocks, gaining entry to a peer group, or successfully riding a tricycle. The construct of executive function is difficult to define, in part, because executive function, attention, and memory are interdependent and have fuzzy boundaries (Lyon, 1996). Despite difficulty in establishing a clear definition, there is growing consensus among researchers as to what executive functions entail: self-regulation, sequencing of behavior, flexibility, response inhibition, planning, and organization of behavior (see Eslinger, 1996). Control and modulation of behavior are fostered by the abilities to initiate, shift, inhibit, sustain, plan, organize, and strategize (Denckla, 1989).

Emerging Capacities for Executive Functioning

Early researchers did not study executive functioning in young children, believing that executive skills were not functional until the brain reached maturity in adolescence (Golden, 1981). It is now generally recognized that early precursors of these skills are present in infancy (Welsh and Pennington, 1988), and there is a growing body of research that demonstrates that performance on executive tasks improves in a stage-like manner that coincides with growth spurts in frontal lobe development during infancy and through the early childhood years (Anderson, 1998; Bell and Fox, 1992, 1994; Levin et al., 1991; Posner et al., 1998; Thatcher, 1991; Welsh and Pennington, 1988). This evidence for the early emergence of executive skills is further supported by findings from the neuropsychologi-



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