Separation Anxiety Disorder (SAD) is an anxiety disorder in which an individual experiences excessive anxiety regarding separation from home and/or from people to whom the individual has a strong emotional attachment (e.g., a parent, caregiver, significant other, or siblings). Separation anxiety is a natural part of the developmental process. It is most common in infants and little children, typically between the ages of six months to three years, although it may pathologically manifest itself in older children, adolescents and adults. Unlike SAD (indicated by excessive anxiety), normal separation anxiety indicates healthy advancements in a child's cognitive maturation and should not be considered a developing behavioral problem.

According to the American Psychiatric Association (APA), Separation Anxiety Disorder is an excessive display of fear and distress when faced with situations of separation from the home and/or from a specific attachment figure. The anxiety that is expressed is categorized as being atypical of the expected developmental level and age. The severity of the symptoms ranges from anticipatory uneasiness to full-blown anxiety about separation.

SAD may cause significant negative effects within areas of social and emotional functioning, family life, and physical health of the disordered individual. The duration of this problem must persist for at least four weeks and must present itself before a child is eighteen years of age to be diagnosed as SAD in children, but can now be diagnosed in adults with a duration typically lasting six months in adults as specified by the DSM-5.

The origins of separation anxiety disorder stem from attachment theory which has roots in the attachment theories both of Sigmund Freud and John Bowlby. Freud's attachment theory, which has similarities to learning theory, proposes that infants have instinctual impulses, and when these impulses go unnoticed, it traumatizes the infant. The infant then learns that when their mother is absent, this will be followed by a distressing lack of gratification, thus making the mother's absence a conditioned stimulus that triggers anxiety in the infant who then expects their needs to be ignored. The result of this association is that the child becomes fearful of all situations that include distance from their caregiver.

John Bowlby's attachment theory also contributed to the thinking process surrounding separation anxiety disorder. His theory is a framework in which to contextualize the relationships that humans form with one another. Bowlby suggests that infants are instinctively motivated to seek proximity with a familiar caregiver, especially when they are alarmed, and they expect that in these moments they will be met with emotional support and protection. He poses that all infants become attached to their caregivers, however, there are individual differences in the way that these attachments develop. There are 4 main attachment styles according to Bowlby; secure attachment, anxious-avoidant attachment, disorganized attachment, and anxious-ambivalent attachment. Anxious-ambivalent attachment is most relevant here because its description, when an infant feels extreme distress and anxiety when their caregiver is absent and does not feel reassured when they return, is very similar to SAD.

As with other anxiety disorders, children with SAD tend to face more obstacles at school than those without anxiety disorders. Adjustment and relating school functioning have been found to be much more difficult for anxious children. In some severe forms of SAD, children may act disruptively in class or may refuse to attend school altogether. It is estimated that nearly 75% of children with SAD exhibit some form of school refusal behavior.

There are several possible manifestations of this disorder when the child is introduced into an academic setting. A child with SAD may protest profusely upon arrival at school. They might have a hard time saying goodbye to their parents and exhibit behaviors like tightly clinging to the parent in a way that makes it nearly impossible for the parent to detach from them. They might scream and cry but in a way that makes it seem as though they were in pain. The child might scream and cry for an extended period of time after his or her parents are gone (for several minutes to upwards of an hour) and refuse to interact with other children or teachers, rejecting their attention. They might feel an overwhelming need to know where their parents are and that they are okay.

This is a serious problem because, as children fall further behind in coursework, it becomes increasingly difficult for them to return to school.