The second independent samples t-test was conducted to compare the scores of the experimental and control groups two weeks after the treatment (post-test 2). As indicated in Table 2, there is a significant difference between the gain scores for the experimental group (M = 16.97, SD = 1.64) and the gain scores for the control group (M = 14.56, SD = 2.72; t (38) = 3.39, p < .05). This final result shows that the mean increment of the experimental group two weeks after the treatment is more than the control group. That is, the participants who received memory strategy instruction learned significantly more vocabulary than others. Since there is a significant difference between the means of the two groups, the null hypothesis (teaching EFL vocabulary through memory strategies has no significant impact on learners' long-term vocabulary retention) is rejected. Therefore, the DPH is supported.