Six curriculum-based measures of math performance were developed for use with 4-year-old preschool children. Measures included counting objects, selecting numbers, naming numbers, selecting shapes, counting, and visual discrimination. Technical properties of probe scores were assessed in two rural public preschool programs. Alternate forms, source, and item reliability of probe scores were assessed with approximately 50 children per probe. A randomly selected sample of 53 children participated in the validation phase of the study. Concurrent validity of probe scores was assessed with the Brigance Screens and the Test of Early Mathematics Ability. Four of the probes yielded reliable and meaningful estimates of early math skills. Additional research is needed to evaluate the degree to which the probes are sensitive to growth and useful within comprehensive curriculum-based assessment models.