This is the best information on explanation of subtests that I’ve found. It’s long, but very informative:
Verbal Subtests
Information - (1) Fund of general knowledge; (2) Factual knowledge, long-term memory, recall; (3) This measures how much general information the child has learned from school and at home.
Similarities - (1) Verbal abstract reasoning; (2) Abstract reasoning, verbal categories and concepts; (3) This measures the child’s ability to think abstractly. The child decides how things are different or alike.
Arithmetic - (1) Numerical reasoning, attention and short-term memory for meaningful information; (2) Attention and concentration, numerical reasoning; (3) This is not pencil-and-paper arithmetic. Rather it measures verbal mathematical reasoning skills by giving the child oral problems to solve.
Vocabulary - (1) Knowledge of word meanings; (2) Language development, word knowledge, verbal fluency; (3) The child explains that a word means by defining or describing what it does. The dictionary definition is not the only acceptable answer.
Comprehension - (1) Social comprehension and judgment; (2) Social and practical judgment, common sense; (3) This measures how well your child can think abstractly and understand concepts
[Digit Span] - (1) Short-term auditory memory for non-meaningful information; (2) Short-term auditory memory, concentration; (3) This measures a child’s ability to remember a sequence of numbers (both backwards and forwards). This sub-test is optional and does not have to be included in your child’s assessment
Performance Subtests
Picture Completion - (1) Attention to visual detail; (2) Alertness to detail, visual discrimination; (3) The child looks at pictures and tells the examiner what part is missing
Coding - (1) Visual-motor skills, processing speed; (2) Visual-motor coordination, speed, concentration; (3) This section measures a child’s ability to decipher a code and copy the correct symbols in a controlled period of time.
Picture Arrangement - (1) Attention to visual detail, sequential reasoning; (2) Planning, social logical thinking knowledge; (3) This requires a child to put pictures in order so that the story they tell makes sense. It measures their ability to create the whole from its parts.
Block Design - (1) Visual abstract ability; (2) Spatial analysis, abstract visual problem-solving; (3) Unlike picture arrangement, where the child is given the parts and makes up the whole, this test measures the child’s ability to look at the whole first, then break it into parts, and finally to reconstruct the whole. It provides blocks and pictures, and the child must put the blocks together to re-create what’s in the picture of the blocks
Object Assembly - (1) Part-whole reasoning; (2) Visual analysis and construction of objects; (3) The child is given puzzle parts and must complete the puzzle. It measures a child’s ability to make a whole out of its parts.
[Symbol Search] - (2) Visual-motor quickness, concentration, persistence (note: new with WISC III)
[Mazes] - (1) Graphomotor planning, visual-motor coordination and speed; (2) Fine motor coordination, planning, following directions; (3) The child has to find the way out of a maze by using a pencil. Performance is also based on time.