“…In direct response to the three research questions of the study, findings have revealed 1) an overall poor performance in orally producing English if clause sentences by the participants, 2) the verbs which were not backshifted for type II and III if clause as their general mistakes, and 3) a significant difference in applying certain LLSs between successful and less successful students. The first set of findings confirms the tremendous difficulty of English if clause experienced by Thai EFL students as also reported by previous research (Suraprajit, 2022;Yossatorn et al, 2022;Suteerapongsit and Pongpairoj, 2020;Katip and Gampper, 2016;Hinnon, 2015;Pengpanich, 2014), and even to a greater extent when they had to produce it spontaneously while speaking. Second, the fact that the mistakes were generally intralingual in nature indicates a certain level of knowledge about this English grammatical structure possessed by the participants although it is yet incomplete.…”