Soft signs are broader, nonspecific neurological impairments, or symptoms, such as impaired fine motor skills, neurosensory hearing loss, poor gait, clumsiness, and poor hand - eye coordination. Many soft signs have norm-referenced criteria, while others are determined through clinical judgment. "Clinical judgment" is only as good as the clinician, and soft signs should be assessed by either a pediatric neurologist, a pediatric neuropsychologist, or both. Functional
When structural or neurological impairments are not observed, all four diagnostic systems allow CNS damage due to prenatal alcohol exposure to be assessed in terms of functional impairments. Functional impairments are deficits, problems, delays, or abnormalities due to prenatal alcohol exposure (rather than hereditary causes or postnatal insults) in observable and measurable domains related to daily functioning, often referred to as developmental disabilities. There is no consensus on a specific pattern of functional impairments due to prenatal alcohol exposure and only CDC guidelines label developmental delays as such, so criteria (and FASD diagnoses) vary somewhat across diagnostic systems.
Representative examples include:

Learning impairments are associated with impaired dendrites of the hippocampus
Impaired motor development and functioning are associated with reduced size of the cerebellum
Hyperactivity is associated with decreased size of the corpus callosumFunctional difficulties may result from CNS damage in more than one domain, but common functional difficulties by domain include: Note that this is not an exhaustive list of difficulties. Achievement: Learning disabilities
Adaptive behavior: Poor impulse control, poor personal boundaries, poor anger management, stubbornness, intrusive behavior, too friendly with strangers, poor daily living skills, developmental delays
Attention: Attention-Deficit/Hyperactivity Disorder (ADHD), poor attention or concentration, distractible
Cognition: Intellectual disability, confusion under pressure, poor abstract skills, difficulty distinguishing between fantasy and reality, slower cognitive processing
Executive functioning: Poor judgment, Information-processing disorder, poor at perceiving patterns, poor cause and effect reasoning, inconsistent at linking words to actions, poor generalization ability
Language: Expressive or receptive language disorders, grasp parts but not whole concepts, lack understanding of metaphor, idioms, or sarcasm
Memory: Poor short-term memory, inconsistent memory and knowledge base
Motor skills: Poor handwriting, poor fine motor skills, poor gross motor skills, delayed motor skill development (e.g., riding a bicycle at appropriate age)
Sensory processing and soft neurological problems: sensory processing disorder, sensory defensiveness, undersensitivity to stimulation
Social communication: Intrude into conversations, inability to read nonverbal or social cues, "chatty" but without substance

Secondary disabilities
The secondary disabilities of FAS are those that arise later in life secondary to CNS damage.