The present study investigates the effect of a teacher training program on promoting learners' Self-Directed Learning Strategies. Moreover the study specifically attempts to investigate the effect(s) of learners' Self-Directed Learning Strategies on their language achievement. The study is quasi-experimental in nature, the population consisted of post-basic grade eleven female students registered in the academic year 2009-2010. Eight post-basic grade eleven classes of a total of two hundred students from three different girls' schools in Muscat region represented the sample of the study. Four classes represented the experimental group which was instructed by trained teachers using the developed activities. The other four classes represented the control group, which were taught the common way. Three types of instruments were used for the purpose of this study. First, a Self Directed Learning Strategies' Inventory was used to assess the learners' SDL Strategies. Second a Language Achievement Test was used to measure the learners' language achievement. Finally a Semi Structured Interview was used to support the study findings. The instruments were validated and tested for reliability, Two major findings were concluded from this study. First, the results of the SDL inventory revealed that there was no significant difference in the SDL Strategies for the experimental group after the experiment. Second, the results of the Language Achievement Test revealed a significant difference between the learners' achievement of the experimental group and the learners' achievement of the control group that favored the experimental group who were taught by trained teachers using the developed activities. In the light of the findings, implications and a number of recommendations were suggested to promote SDL Strategies.