The program's basic concept was simple: Each letter of the English alphabet was represented by a unique character with traits derived from itself. The consonants were males (as "the Letter Boys"), and the vowels were females (as "the Letter Girls", whom there could be no word without). Reiss-Weimann, Friedman, and Callen also wrote two series of books about the characters, "Fables from the Letter People" and "Read-to-Me". Each Letter Person also had an accompanying song (available on 8-track cartridge and vinyl record), and inflatable vinyl effigies in two sizes or a.k.a. "life-size") known as "Huggables". Other merchandise included filmstrips and flash cards. Educators who adopted the program were trained in its implementation, and "The Letter People" was soon picked up by hundreds of schools across the US.