The aim of this study was to investigate the quantity and quality of written activities based on critical thinking skills in the English language textbooks for Grades 6 and 10 in Oman. The study also determined the quality of questions posed by teachers during classroom writing lessons and their ability to stimulate critical thinking. Another aim of this study was to investigate whether writing in English was an obstacle to students' use of critical thinking skills. The research sample consisted of female English language teachers and students from five public schools in Muscat Governorate: from Grade 6 - four teachers and nine students and from Grade 10 - four teachers and nine students. The researcher used a content analysis checklist to analyze the textbooks and conducted classroom visits followed by interviews with the teachers. The study also included a writing test for students from both grades followed by a Retrospective Think-Aloud Protocol. The study answered the following research questions: 1. To what extent does the English for Me textbooks for Grades 6 and 10, as depicted in students' textbooks, cater for critical thinking in writing? 2. To what extent do Grades 6 and 10 teachers incorporate critical thinking skills into writing lessons? 3. How does L1/L2 influence critical thinking skills in writing for Grades 6 and 10 students? The results of the analysis, interviews and written tests revealed the following: 1. The sixth grade textbooks lacked components to develop critical thinking, while the tenth grade textbooks contained 20% of activities that stimulated critical thinking. Sixth grade writing classes did not contain critical thinking questions, while some writing classes for Grade 10 included questions that stimulated critical thinking. 2. The ability of sixth graders to use critical thinking skills varied, while most of the tenth grade students demonstrated the ability to use critical thinking skills during classroom observations. 3. Grade 10 showed better critical thinking skills in the open-ended writing test in comparison use to grade 6 students. Most students commented that the lack of vocabulary needed was the hindrance.