Based on Larsen-Freeman’s (2001) three-dimensional (form-meaning-use) framework of grammar teaching, this study aimed to investigate which type of clause (noun, adjective or adverbial) is the most challenging for second/foreign language (L2) learners in writing skills. Depending on the results of a diagnostic test prepared in accordance with the form-meaning-use triangulation, Noun Clauses (NCs) were found to be the most challenging type for students studying in the Department of English Language Teaching at a state university in Turkey. Then a NCs test grounded on the same framework was given to the students as the pretest to examine their available knowledge of NCs. After the pretest, the students went through a nine-hour intensive treatment phase consisting of three sessions to instruct NCs with regard to the form-meaning-use framework. The treatment stage was followed by the posttest to examine the progress that students had made during the treatment phase. The findings revealed a remarkable improvement in the students’ knowledge of NCs in writing skills, which showed that the form-meaning-use framework enables effective and efficient instruction in the language classroom. It was also found that the students’ L2 proficiency had a significant effect on their knowledge and performance of using NCs in writing skills
