Although many students who enter kindergarten are cognitively ready to meet the demands of the kindergarten mathematics curriculum, some students arrive without the early abstract reasoning abilities necessary to benefit from the instruction provided. Those who do not possess key cognitive abilities, including understandings of conservation, insertions into series, and the oddity principle, are at a disadvantage when attempting to master mathematical concepts and skills that require early abstract thought. Recognizing the need to address this gap, this study examined the effects of an intervention designed to teach children conservation, insertions into series, and the oddity principle. The study included 78 kindergartners enrolled in a culturally, linguistically, and socioeconomically diverse metropolitan school district. Students were randomly divided among one of three groups: cognitive intervention, numeracy instruction, and art instruction. Instruction for each group was matched in number, timing, and extent of sessions. The study found that kindergartners who received the cognitive intervention scored significantly higher on measures of cognitive ability than those in the comparison group who participated in the art instruction or those who received numeracy instruction. On the Woodcock-Johnson III Applied Problems scale, those in the cognitive intervention scored significantly higher than those who received art instruction. Those in the cognitive intervention and those in the numeracy intervention performed similarly. These results suggest that it is possible to provide instruction that enhances the cognitive abilities of kindergartners who do not possess key reasoning abilities. In addition, there is evidence that promoting early abstract thought can enhance kindergartners' mathematical abilities. (Contains 4 tables.)