© 2019, Association for Behavior Analysis International. The Relational Abilities Index (RAI) has shown considerable utility as a functional proxy measurement of intellectual performance by providing a metric of an important skill set known as relational skills, which are proposed to underlie much of what we conceive of as intellectual behavior. The Relational Abilities Index+ (RAI+) assesses performance across an extended range of relational skills (Same/Opposite, More/Less, Same/Different, Before/After, and Analogy), and has been designed to provide a more comprehensive and nuanced assessment of relational skills. The current study aims to investigate the validity and utility of the RAI+ by assessing its degree of correlation with well-established assessments of intelligence (WASI), numeracy (WAIS: Arithmetic), and educational attainment (WIAT-T-II). Results indicate that the RAI+ displays considerable efficacy in predicting intellectual performance and numeracy, but not educational attainment.