Among the major initials of any language program is the specification of content of language teaching and learning in developing materials. As the aim of content specification is to prepare the list of items in the order they will be taught, different factors like the environment in which the course will be used, needs of the learners, and teaching and learning principles should be taken into account (Nation & Macalister, 2010). Therefore, the process of content specification maximizes the interaction between the input or content, learner, and learning process. In curriculum development, once the input is determined, issues concerning the content and design of classroom activities and materials should be addressed (Kumaravadivelu, 2006).

Based on the principles of language teaching and learning, the content of a language lesson may mainly focus on language, functions, topics and themes, genre, skills and subskills, situations and roles, strategies, or task outcomes which are called units of progression. In a language-centered curriculum, in the area of grammar, choices have to be made regarding the units of vocabulary, grammar, verb forms, verb patterns, sentence patterns, or language functions. In a learner-centered curriculum, in the area of task, the most appropriate pedagogic tasks are determined through needs analysis. The tasks provide language samples to learners and allow negotiation of difficulty (Nation & Macalister, 2010). Therefore, depending on the goal of a language lesson, certain units of progression might be used to select and sequence the materials in a course.