Sensory processing is not something that can be directly measured, since it is a purely subjective area. We cannot see how things appear to another person, or hear how different noises sound. Children often lack the vocabulary and the point of reference to describe how they are experiencing the world. Therefore, we are limited to observing responses to different sensations and looking for evidence of difficulty making good use of sensory input. For example, if a child has a hard time standing on one foot, we can theorize that they may not be integrating their sense of gravity's pull, or of their awareness of their own position in space, or both. We can then further investigate similar areas through other observed activities and assemble a picture of ability and difficulty, "detective-style." There are very few standardized or normative tests that assess sensory integration or processing:

The Sensory Integration and Praxis Test (SIPT) is a standardized battery of tests to get an in-depth look at various aspects of sensory processing in order to assess sensory integration dysfunction. It can be used on children four 8 years, 11 months of age. It takes several hours to administer the whole test and requires extensive and expensive training to learn to administer it. Therapists who complete this training (through Western Psychological Services) are certified and listed in a database. Because of the commitment required to become certified, it can be difficult to find a therapist in your area who is trained to administer this test. Some therapists use subtests from this tool (or from its precursor, the Southern California Test of Sensory Integration) as informal tools to look at specific aspects of sensory processing such as motor planning or bilateral integration in motor skills.

The Sensory Profile is a standardized tool for measuring sensory abilities and the effect those abilities have on functional performance in children three to ten.  It is a judgment-based questionnaire that evaluates how a child responds to visual, auditory, touch, taste, movement, and multi sensory stimuli. A classification system based on means is used to rate the child’s responses in comparison to a normative sample of children. It is helpful in determining whether there is a strong pattern of over- or under-responsiveness to sensory input in general, as well as in which areas those atypical responses are most often seen. There is also a School Companion Sensory Profile which is usually given to teachers; it doesn't include a lot of the questions that would be seen at home but not at school ("exhibits distress during grooming," for example).  Now there is also an Adult/Adolescent Sensory Profile, which I sometimes use interview-style with young teens or pre-teens to assess their awareness and perception of their own sensory preferences, as well as an Infant/Toddler Sensory Profile.

The Test of Sensory Functions in Infants was developed by early childhood specialists Georgia DeGangi, PhD, OTR and Dr. Stanley Greenspan, (well known for his approach in working with children called "floor time").  It assesses five areas of sensory function (reactivity to tactile deep pressure, adaptive motor functions, visual-tactile integration, ocular-motor control, and reactivity to vestibular stimulation) in children from four to eighteen months of age. Each item is scored via a numerical rating scale and results in "normal," "at risk," or "deficient" scores (an older test with not-so sensitive terms).

In addition, therapists often use standardized motor skills tests such as the Peabody Developmental Motor Scales, 2nd ed. (PDMS-2), for children birth to six years of age, or the Bruininks-Oseretsky Test of Motor Performance (TMP). The TMP has not been re-normed in many years and so is of questionable validity. Unfortunately, there are scarce options for standardized motor skills tests for children older than six years.

Often, therapists will use informal assessment methods to investigate sensory processing and integration. These can include structured observations, such as asking a child to try to imitate positions, hand placements, or gestures without looking at their own body. Or watching a child navigate an unfamiliar obstacle course while noting how quickly and adeptly he is able to move himself under/over/through the equipment. Both of these observations would assess motor planning, and both would require familiarity with typical development of motor skills for comparison. As a guide to assessing sensory integration through observation, A. Jean Ayres published a form called "Clinical Observation of Sensory Integration" in 1975. It includes such observations as eye movements across body midline, holding of trunk flexion and extension against gravity, and the presence or absence of tonic neck reflexes.  More recently, Winnie Dunn, M.Ed., OTR incorporated some of these observations and used a normative population of 263 children to come up with some broad guidelines for Kindergarten-aged children, published as A Guide to Testing Clinical Observations in Kindergarteners.

Other observations could include directly observing responses to typically non-aversive sensations. For example, if a child covers her ears when the bathroom fan goes on, comments on the ticking of a quiet clock, seems afraid of a fuzzy stuffed animal, or strongly avoids letting his feet come off the ground while sitting on a swing, a therapist would note that and look for patterns.

Finally, an interview with caregivers and/or teachers about their observations, concerns, and reports of typical behaviors and abilities can be an important piece of the puzzle. No one knows a child better than the people who spend every day with her. A therapist can help gather information and help with the detective work of assessing sensory processing.