This study was firstly aimed to develop the Foreign Language Substance Group Curriculum for enhancing students' four English skills required to promote learning in the different areas of subject. It used Marzano's Taxonomy as a framework for curriculum design. To articulate this framework, the study used content-based instruction (CBI) to pave a way for the meet of academic contents and colorful English experiences. Population of the study were the sixth grade primary students of Lakmuang Mahasarakham School located in the Northeastern of Thailand. Development procedures went through four stages. The first stage required fundamental data relating to the population's needs and interests. In the second stage, the curriculum was drafted. Different curriculum materials were developed as well. Prior to use, the curriculum and its materials were brought to the experts for suggestions to ensure their quality. In the third stage, the curriculum was implemented to the 40 primary students in the sixth grade purposively selected from the population mentioned. In this stage, the one group time-series design was adopted. In the last stage, the curriculum was required to determine its efficiency including being revised. The findings were four dimensions. Post-test score of both achievement test and unit test were significantly higher than the pre-test score. The metacognition and self-system were reported positively. The efficiency index of the curriculum developed was higher than the established requirement. The students' opinion toward the curriculum was positive. Additionally, the students' English skills were supported. (Contains 1 table and 1 figure.)