In a multiple baseline design, a teenager with a mental age of four years was taught two abstractions. One was the oddity principle (selecting the one object in a group which differs from the rest). The other was seriation (aligning objects along a continuum of size, and inserting new objects into their proper places in the alignments). These abilities demarcate the transition between preoperational and concrete operational thought, and are the earliest forms of purely relational responding. Learning sets of 80 oddity problems and 65 seriation problems were used to promote generalization. A "fade-out" procedure was used to make mastery of the problems as easy as possible. Combination of these techniques produced the first recorded success in teaching either the oddity principle or seriation to a child with severe disabilities, and may substantially reduce difficulty of helping many such children learn concepts at this level of abstraction.