This article is aimed at evaluating the possibility that Set I of the Advanced Progressive Matrices (APM-Set I) can be employed to assess fluid ability in a short time frame. The APM-Set I was administered to a sample of 1,389 primary and secondary school students. Confirmatory factor analysis attested to the unidimensionality of the scale. Item response theory analyses were applied to investigate the increasing level of item difficulty, test information function, and differential item functioning across gender and age. Additionally, validity measures are reported. Results provide evidence that the APM-Set I can be used as a reliable and valid short form of the Raven's Progressive Matrices in the assessment of fluid ability. (Contains 2 figures, 2 tables, and 6 footnotes.)