I'm not sure this answers you question, but I'll do my best.
BabyCenter's developmental psychologist had this to say:
When evaluating your child's level of self-control, take her temperament into account. This is an age where there may be a wide range of individual differences; some children are naturally more impulsive and less reflective than others. More impetuous children may need extra guidance and reminders, especially in exciting or distracting situations. Similarly, more reflective children may appear more self-controlled, when in fact, they're just more reserved.
Children having difficulty with self-control can benefit from more structured situations and adult coaching. This ability develops with maturity and practice, so although you may be tempted to reprimand your child when she can't control herself, bear in mind that punishment isn't effective in this situation.
She also added:
School-age children show high levels of self-control compared to their younger counterparts. At this age, they can understand the reasoning behind rules so they're more willing and able to conform to parents' and teachers' expectations. They also have a strong sense of fairness, so appealing to what is fair can often overcome their own self-interests.
And, finally, she points out:
Preschoolers work very hard developing self-control and make great strides during these years. They're capable of delaying gratification for short periods of time and when they're not overwhelmed by emotion, they can use words instead of actions to express their feelings and desires.
Demonstrating self-control is quite challenging at this age; kids are still practicing their skills and need a great deal of guidance (and patience) from adults. Providing your child with strategies and giving him reminders is more effective than punishing him for mistakes. Explaining to your son why he can't have a toy he sees in a store, reminding him of the toys he already has at home, and suggesting that he put the toy on his "wish list" are all effective ways of helping him control his strong feelings. Simply saying "no" or threatening punishment if he protests will not give him the mental strategies to cope with the situation. Likewise, teaching your son to use words to ask another child for a toy or a turn on a ride is more effective than just telling him not to grab. Because young children learn through repetition, you may need to remind your son many times before he can control his impulses on his own.
She also consistently cautions that extreme states -- fatigue, hunger, emotional moments -- are often when children have the most trouble maintaining their self control. In my humble opinion, that's not a characteristic limited to children; I get antsy and upset easily when I'm hungry as well.
Also see this larger question.