The effectiveness of the CIRCUS language instruments for determining language comprehension and performance in the 4- and 5-year-old child is discussed. In these instruments, the use of content words is primarily studied through the use of single-word measures, such as a picture vocabulary test and an auditory discrimination test, whereas the use of functor words is studied by three different measures: a listening comprehension test, a test which measures the receptive understanding of certain grammatical constructions, and a test which measures the ability of the child to produce the same or similar constructions. These last two measures are designed to provide information which can be used to compare the child's receptive vs. productive use of grammatical structures. The intent of the CIRCUS measures is to provide the teacher with a reasonable sampling of the child's language. The CIRCUS instruments measure the growth of the child's spoken language by observing three types of language use: descriptive, functional, and narrative. (DB)