Assessment of learners affects all processes of their learning. Generally, without assessment, it is very difficult to evaluate the effectiveness of the teaching and learning process. Understanding their weak points and difficulties in their writing would help teachers and administrators focus more on these areas. Therefore, this content analysis study was an attempt to investigate the relative contribution of each writing component to the variation in the overall writing performance of TEFL undergraduate students to determine areas of strength and weakness in their writing. To this end, the writing samples of 73 students who were willing to participate in this study at different universities in Tabriz, Iran, were assessed through an Analytical Scoring Scale. These participants were divided into two groups: group 1, first-year and second-year students, and group 2, third-year and fourth-year students. The results of the Stepwise Multiple Linear Regression analysis revealed that the greatest contributions to the variance of the total rating of TEFL undergraduate students' writings were related to the grammar and punctuation components in groups 1 and 2, while the least contributions were related to the content and spelling in group 1, and vocabulary and spelling in group 2. In addition, the results indicated that the weaknesses and issues of participants in both groups of this research were mostly related to the grammatical structure and using punctuation marks in paragraphs. Moreover, the positive effects of the analytical scoring scale as well as the implications of the findings were discussed.