The present study investigates the effect of the first language (L1) on learners by using the negative and the positive evidence in the classrooms while teaching English directional prepositions such as 'to' and 'into'. It is assumed that Arabic has two versions of 'to'. It has the directional interpretation without boundary-crossing which is equivalent to the English 'to'; whereas, it also denotes a similar interpretation to English directional preposition 'into' which is unavailable in Arabic and involves boundary-crossing. The study considers two groups to examine the effect of the overlaps, who are at an intermediate stage of development; the experiment group (E.G.) and the control group (C.G.). The control group is the base to measure the effectiveness of the treatments on the experiment groups' judgments. Hence, an Acceptability Judgment Task is devised to elicit participants' judgments on the task items in the pretest and the posttest. Results show clear advantage of the negative evidence in the experiment group's performance in the posttest in learning 'to' with and without boundary-crossing. There is a difference in the experiment group's performance in the posttest in learning 'into' with the boundary-crossing event after receiving the positive evidence. Similarly, a difference was observed in the experiment group's judgment with those of the control group in the comparison between 'to' and 'into' with the boundary-crossing event in the posttest.