This study investigated the effect of individual differences (IDs) like language proficiency, gender and age on careful, unpressured online planning on the production of speech act of apology in institutional discourse. For this purpose, one hundred and eighty-seven Persian EFL university students at three academic levels (undergraduates, postgraduates and PhD students) participated and cross-sectional data were collected to compare and analyze the apologies produced by learners at different proficiency levels. A three way between subject analyses (ANOVA) showed quantitative differences among the three groups according to individual differences. Further, in-depth qualitative analyses of test items and retrospective verbal reports (RVRs) taken from the participants revealed developmental information about the series of processes, language states and patterns followed by learners when making an apology in a second language. Sociocultural, socio-psychological and socio-affective aspects of the discourse situations influenced not only students’ pragmalinguistic and sociolinguistic choices but also their negotiation of lexical and grammatical choices in planning the speech act of apology. Apparently, the degree of sociocultural accommodation to the L2 pragmatic norms may be a matter of choice as of ability. One major pedagogical implication of this study is that any account of the development of interlanguage pragmatics (ILP) should take into consideration the interaction of ID variables that are likely to intervene between the stages of noticing and target like production.<br /> <strong> </strong><br />