Interviewing both child and parent separately allows for the clinician to compile different points of view and information.Commonly used interviews include:
Anxiety Disorders Interview Schedule for the DSM-IV, Child Parent Versions (ADIS-IV-C/P)
Diagnostic Interview Schedule for Children, Version IV (DISC-IV)
Schedule for Affective Disorders and Schizophrenia for School-aged Children-Present and lifetime version IV (K-SADS-IV)

Self-report measures
This form of assessment should not be the sole basis of a SAD diagnosis. It is also important to verify that the child who is reporting on their experiences has the cognitive and communication skills appropriate to accurately comprehend and respond to these measurements. An example of a self-report tool that has been tested is: The Separation Anxiety Assessment Scale for Children (SAAS-C). The scale contains 34 items and is divided into six dimensions. The dimensions in order are:  Abandonment, Fear of Being Alone, Fear of Physical Illness, Worry about Calamitous Events, Frequency of Calamitous Events, and Safety Signal Index. The first five dimensions have a total of five items while the last one contains nine items. The scale goes beyond assessing symptoms; it focuses on individual cases and treatment planning. Observation
As noted by Altman, McGoey & Sommer, it is important to observe the child, "in multiple contexts, on numerous occasions, and in their everyday environments (home, daycare, preschool)".
As each situation is dealt with masterfully, the child advances to the next phase of intensity. This pattern continues until the child is able to handle being away from their parent in a developmentally typical way that causes them and their caregiver(s) minimal amounts of stress. While there is some controversy about using exposure therapy with children, it is generally agreed upon that exposure therapy in the context of SAD is acceptable as it may be the most effective form of therapy in treating this disorder and there is minimal risk associated with the intervention in this context. Contingency management
Contingency management is a form of treatment found to be effective for younger children with SAD. Contingency management revolves around a reward system with verbal or tangible reinforcement requiring parental involvement. A contingency contract is written up between the parent and the child, which entails a written agreement about specific goals that the child will try to achieve and the specific reward the parent will provide once the task is accomplished. When the child undergoing contingency management shows signs of independence or achieves their treatment goals, they are praised or given their reward. This facilitates a new positive experience with what used to be filled with fear and anxiety. Children in preschool who show symptoms of SAD do not have the communicative ability to express their emotions or the self-control ability to cope with their separation anxiety on their own, so parental involvement is crucial in younger cases of SAD.