The purpose of PDDNOS assessment is twofold: to gather information to formulate an accurate diagnosis and to provide information that will form the basis of an appropriate intervention plan for the individual child and family. Assessment of PDDNOS usually includes the following elements:
Medical assessment. The medical evaluation should include a thorough birth, developmental, medical, and family history, and a full physical and neurological examination. Not all children with PDDNOS require laboratory tests such as a chromosome study, including a test for Fragile X, an EEG (which measures the brain's electrical activity), or a brain scan such as MRI (an X-ray that gives a picture of the brain's anatomy). The primary care physician determines if these are needed. Although the cause of PDDNOS is generally unknown, the physician may discuss some medical conditions that do not cause PDDNOS but tend to be found in such children-- for example, seizure disorder. Associated conditions can cause or worsen a child's problems.
Interviews with the parents, child, and child's teacher. A child with PDDNOS may exhibit different abilities and behaviors in different settings or situations. Parents and teachers can provide information about behaviors not observed during the formal testing sessions.
Behavior rating scales. Checklists of possible problems should be completed by parents or caretakers familiar with the child. Many diagnosticians use the checklist for autism. However, no scale has yet been developed specifically to determine the diagnosis of PDDNOS.
Direct behavioral observations. The child's behavior is recorded as it happens, and assessment results are often graphed to aid interpretation. This type of assessment can be carried out either in an artificial situation (e.g., a child taking an intelligence test) or in a natural situation (e.g., a child's home or classroom).
Psychological assessment. The psychologist uses standardized instruments to evaluate the child's cognitive, social, emotional, behavioral, and adaptive functioning. Parents learn in which areas of development their child exhibits delays.
Educational assessment. Both formal assessment (such as the use of standardized tests) and informal assessment (such as direct observation and interviewing the parents) should be used to evaluate the child on the following points:

• pre academic skills (e.g., shape and letter naming),
• academic skills (e.g., reading and arithmetic),
• daily living skills (e.g., toileting, dressing, eating), and
• learning style and problem-solving approaches.

Communication assessment. Formal testing, observational assessment, and interviewing the child's parents are all useful strategies for assessing communication skills. It is important to assess a range of communication skills, including the child's interest in communication, why (for what purpose) the child communicates, the content and context of the communication, how the child communicates (including facial expression, posture, gestures, etc.), and how well the child understands when others communicate with him or her. Assessment results should be used when designing a communication program for the child. This may incorporate one or more alternative forms to spoken communication, such as sign language and/or using a communication board (i.e., pointing to pictures to express oneself).
Occupational assessment. An occupational therapist may evaluate the child to determine the nature of his or her sensory integrative functioning: how the child's different senses- hearing, sight, taste, smell, touch-- work together. Standardized tools are used to assess fine motor skills (such as using fingers to pick up small objects), gross motor skills (such as running and jumping), whether the child is right or left handed, and various visual skills (such as depth perception).