The CIRCO project is a large scale effort to design a series of diagnostic instruments, based on the CIRCUS tests, for Spanish-speaking children in preschool, kindergarten, and first grade classrooms in the United States. The goal is to develop measures with the following characteristics: (1) is suitable for use with Spanish-speaking children from different cultural and language dialect backgrounds; (2) emphasizes a differentiated view of human abilities; (3) eliminates cultural or regional biases, with sufficient pilot testing; (4) has norms representative of the Spanish-speaking population of 4-6 year-old children in preschool programs; (5) considers the construct of Spanish as a language, and the syntax and lexical differences between Spanish and English; (6) adequately guards against test score misinterpretation and test misuse. In both the CIRCUS and CIRCO systems, interpretive scores (such as grade equivalent scores) will be abandoned, and test publishers will provide more direct interpretation with the score report. The plans for pilot testing, field testing, norming, and item review are described. (Author/MV)