The Philippine educational system is adopting a 21st century learning program as one of its frameworks for mainstream and alternative education. It is also known as the Alternative Learning System (ALS). While it is already challenging to realize 21st century learning and its assessment in mainstream classrooms, ALS settings have become more challenging through the years due to the unique circumstances of the students and limited resources and infrastructure. Since teacher quality is one of the determinant factors in assessing ALS skills, looking into these teacher’s beliefs, attitudes, competencies, and classroom practices merits attention. Thus, this study aims to examine the conceptual, praxeological, and socio-emotional dimensions of ALS teachers’ assessment of 21st century skills to better understand their classroom assessment beliefs and practices.