The stimulus equivalence is a fruitful explanatory model in the study of symbolic behavior. However, most experimental studies have simulated the formation of equivalence classes with different populations who present well developed symbolic function. Research is needed to broaden the understanding of the ontogenesis of symbolic behavior. Individuals with restricted previous experimental history, or individuals with minimal verbal repertoires, could provide an appropriate preparation for studying the origins of this behavioral function. In teaching discriminative repertoires, procedures that reorganize the tasks in smaller steps have been successful with populations with atypical development. The same tactics could minimize the difficulties usually found in research on the acquisition of these repertoires in young babies. This study, conducted with three babies (17, 20 and 21 months old), investigated the effects of two procedures during the initial exposure of children to the contingencies of differential reinforcement on simple simultaneous discrimination training. Two participants had a typical development, while the third (P17) presented language delay. Threedimensional visual stimuli (toys) were simultaneously presented in two windows of a motorized apparatus. Each window was part of a rotating cylinder with three compartments; each compartment defined a condition for the window presentation: a) closed with a transparent acrylic; b) closed with a black opaque acrylic; and c) opened. The windows sealed by the transparent acrylic were used for the simultaneous presentation of two stimuli, during which correct response (touching the acrylic window with the stimulus defined as S+) was followed by the rotation of the cylinder and by the opened window. Then, the baby could touch and handle the toy and, during 30-s, the baby and the experimenter played together with it. An incorrect response (touching the window with the S- toy) was followed by the rotation of the cylinder and the presentation of the closed (black) window. In the procedure named S+, only one stimulus was presented on the first four trials. The first and third trials presented the stimulus defined as correct, thus allowing for a correct response and its consequences. The second and fourth trials forced the contact with the incorrect stimulus and with the black, closed window as the consequence. From the fifth trial on, both stimuli were simultaneously presented. The S- procedure began with the two stimuli simultaneously presented and the first response defined the chosen stimulus as the incorrect (S-) for the remaining trials. The S- procedure generated much more errors, with deleterious effects of errors on the learning curves. The babies’ performance in sessions with the S+ procedure alternated correct and wrong responses, but the final section of cumulative curves showed increased correct responding until the learning criterion was attained. The results also suggested that the learning criteria could be reduced from four to three consecutive correct responses. The critical importance of assessment and maintenance of the reinforcing value of stimuli used with babies is also discussed.Procedimentos de ensino de repertórios discriminativos que reorganizam as tarefas em pequenos passos têm tido sucesso com populações com desenvolvimento atípico e podem minimizar, também, dificuldades na investigação sobre a aquisição destes repertórios em bebês menores de 24 meses. Este estudo, conduzido com de três bebês de 17, 20 e 21 meses, verificou os efeitos de dois procedimentos para a exposição dos participantes às contingências de reforçamento diferencial no ensino de discriminações simples simultâneas. Estímulos visuais tridimensionais eram apresentados em um aparato motorizado. No procedimento denominado S+, as quatro tentativas iniciais apresentavam apenas um estímulo: o correto nas tentativas 1 e 3 e o incorreto nas tentativas 2 e 4, possibilitando o contato forçado com as conseqüências diferenciais. A partir da 5a tentativa os dois estímulos passavam a ser apresentados simultaneamente. O procedimento S- previu que o primeiro estímulo escolhido pelo bebê, dentre os dois estímulos comparação, era designado estímulo incorreto. A análise dos acertos e erros acumulados indicou semelhanças no desempenho inicial e intermediário em cada procedimento; maior eficiência do procedimento S+; e efeitos deletérios dos erros nas curvas de aprendizagem. Os critérios de aprendizagem e a manutenção do valor reforçador dos estímulos para os bebês são apontados como variáveis críticas para a eficiência dos procedimentos de ensino.