Gaining proficiency in writing English is essential for long-term success in both academic and professional settings. The lack of contextualized instructional resources, reliance on standard teaching methods, and low student engagement are some of the reasons why developing writing skills among elementary-grade students in the Philippines remains challenging. This research aimed to create and assess a customized learning package specifically designed to improve English writing abilities among Grade 6 students at Guadalupe Elementary School in the Libacao District for the academic year 2024–2025. Recognizing the vital role of proficient writing skills for academic achievement and future employment opportunities, the study addressed key challenges such as limited access to quality educational resources and insufficient exposure to effective writing strategies. Adopting a Design-Based Research (DBR) methodology rooted in constructivist principles, the study employed the ADDIE framework—Analysis, Design, Development, Implementation, and Evaluation—to systematically develop instructional materials focused on essential writing elements: grammar, vocabulary, composition, organization, and style. Pre-test evaluations revealed varying proficiency levels among students, with significant weaknesses in composition and grammar. Following the implementation of the instructional package, post-test evaluations demonstrated notable improvements across all five targeted areas. Additionally, feedback from both students and educators indicated high levels of acceptance and perceived effectiveness of the learning package. This research underscores the value of tailored instructional design in addressing educational challenges and enhancing writing skills among Grade 6 students. Recommendations for future studies include replicating the research in other contexts and conducting ongoing assessments to evaluate the long-term effects of the developed materials.