This study investigated the developmental trajectory of social facilitation and inhibition across 207 participants aged 8-22 in numerosity and phonological comparison tasks. Tested alone or in coaction with a familiar peer, younger participants exhibited social inhibition on reaction times (RT), while a shift toward facilitation occurred around ages 13-14. Analysis of individual RT distributions revealed that peer presence modulated predominant response strategies: younger participants used slower, reactive strategies, while older participants employed faster, anticipative ones. By enhancing the strategy predominating in each age group, peer presence led to social inhibition in children and early adolescents, but social facilitation in mid-adolescents and adults. These findings challenge Zajonc's "dominant response" theory, suggesting that peer presence affects overall decision-making strategies.