T his paper reports a number of crucial implications for the profession of teaching and learning English as a Foreign Language (EFL). Based on his career as an EFL teacher educator, the author presents - in brief  - the conclusions derived from six quasi-experimental researches conducted on the effects of some psycholinguistic variables (i.e.  brain-hemisphericity; personality type; learning style; learning strategies; and multiple intelligences)   on teacher and /or student performance,  Language materials development, learning style-stretch, and language self-efficacy. The first study highlights the  dire need for utilizing the students' full potentials in learning EFL which has become the universally acknowledged means of knowledge production. Currently, most research suggests that we barely use 10% of our brain capacity, yet we can learn to plug in the other 90%. We can learn to tap the reserves of the mind. Language learning strategies enable us to take responsibility for our own learning by enhancing our autonomy and help us assimilate new information more effectively. Geared to this purpose  this study had four major questions: 1) Are there significant differences in the frequency of language learning strategies (LLSs) used by secondary school students in relation to their sex , specialization , and achievement level? 2) Are there significant differences in the type of LLSs used by secondary school students in relation to their sex, specialization, and achievement level? 3) Are there significant differences in brain-hemispheric preferences of secondary school students with respect to their sex, specialization, and achievement level? 4) Are there significant differences among the means of the scores of brain- hemispheric preference groups in their use of LLSs with respect to their sex, specialization and achievement level? Oxford's SILL and Torrance SLT scale were the major instruments used in this study to gather the data from the 642 student sample. Results indicate - among other things - that there are significant differences in the frequency of the LLSs used in favor of female over male students and good over poor students. On the other hand, "cognitive", " metacognitive ", and "memory" strategies were found to be the most popular among Saudi students. The results also revealed that male students favor the left- hemisphere, females favor the integrated mode, and no differences were reported in reference to the right hemisphere. Good students tended to prefer to the left-hemisphere and the integrated mode. Other significant differences among the brain-hemispheric preference groups in their use of LLSs were reported. Results were analyzed, interpreted, and discussed.