The main purpose of this study is to explore the reasons for students' weaknesses in grammar at Jordanian schools, taking as an example the upper basic stage (ages 14-16 years) in the Al-karak district. The study consists of nine chapters; the first three chapters explain the background and context of the study, the teaching of Arabic grammar in Jordan and the heart of the problem together with an outline of previous research. The fourth chapter explains the methodology and procedures of the study. The fifth, sixth, seventh and eighth chapters present the findings of the study and a discussion of the findings. And finally the ninth chapter is the conclusion and recommendations of the study. This chapter points out that some further research is needed in the area of grammar learning and teaching. The methods of data collection were the questionnaire and interview. One questionnaire was developed, directed to the teachers of Arabic and the students of the upper basic stage (eighth, ninth and tenth grades). The interviews were conducted with teachers of Arabic, students and the education supervisors. The sample of the questionnaire was 700 students and 135 teachers. The sample of the interview was 10 teachers, 15 students who were selected upon their willingness to be interviewed. 7 education supervisors who form the whole population were also interviewed. The collected data was analysed based on the frequencies and percentages of the responses. They showed several reasons for students' weaknesses in grammar which attracted high percentages of the participants' acceptance. For instance, 70 per cent of students considered the unavailability of audiovisual aids one of the reasons for their weaknesses in grammar. About half (58.6 per cent) of the students considered the lack of standard Arabic being used by the teachers of other subjects as one of the reasons for the weaknesses. From the teachers' point of view, two reasons attracted the vast majority (89.6 per cent) of their agreement. The first one was students' belief that the formal assessment for students' achievement is lenient. The second one was the lack of previous knowledge of grammar amongst students. The next strong reason for the weaknesses was students' belief that grammar is difficult to understand. Students' carelessness with previous preparation for grammar lessons was also considered one of the strong reasons for the weaknesses in grammar. Education supervisors emphasised that the procedures of teachers appointments are not based on the criteria of teachers' quality and that makes it possible to nominate some teachers who are not able to teach grammar successfully. They also blamed the lack of effective preparation for grammar lessons by the teachers. The supervisors stressed the teachers' weaknesses in grammar. There were many other more subtle reasons for the students' problems which are discussed in depth. The study came up with several recommendations to develop grammar teaching in Jordan as well as some further research related to this study. The original contribution of this study is the combination between the perceptions of students, teachers and education supervisors which enriches the data. It also discussed the procedures of teachers' appointing as one of the issues most neglected by most of the previous studies.