Hello, I would try Pre-Algebra. Mathematics 1 deals with many algebraic skills as well as radicals and exponents, so Pre-Algebra should help to familiarize him with the concepts and help him build the skills he needs. For the geometric portion of Mathematics 1, I would try some of the units from the 8th Grade math course, particularly the Geometric Transformations unit. The Data and Modeling unit from 8th Grade math may also be helpful for some concepts in Mathematics 1.