This research discusses the analysis of students' learning difficulties in understanding cube building material. Mathematics is a basic science that must be studied from an early age because it is closely related to other sciences in order to advance to the next level. The research was created to solve students' learning difficulties at SD Negeri 104208 Cinta Rakyat. This research uses a qualitative approach with descriptive research type. The results obtained are that students still lack understanding of the material that has been presented by the teacher in the process of teaching and learning activities, there are many students who do not understand the material explained by the teacher. It can be seen that students' learning difficulties are also determined by low interest in learning and Lack of understanding of the material taught. Several factors include disinterest in mathematics and ineffective use of learning media. This research suggests that schools are expected to innovate in the use of learning media and learning methods that are changed and adapted to students' learning needs and interests.

The research aims to examine the effectiveness of the STEM-based approach in 21st-century mathematics learning. The STEM-based approach integrates four main disciplines science, technology, engineering, and mathematics into the learning process to enhance critical thinking and problem-solving skills. The STEM approach is highly relevant to developing 21st-century competencies in mathematics education as both focus on the skills required to address complex and dynamic global challenges, such as critical thinking, problem-solving, creativity, communication, collaboration, and digital literacy. The research method employed is a literature review, analyzing relevant theories and previous studies on the topic. The results indicate that the STEM approach can improve the effectiveness of 21st-century mathematics learning, such as enhancing students' technological development skills, analytical abilities, creativity, innovation, and the ability to express ideas and formulate problems. The STEM approach also stimulates students to meet the demands of 21st-century mathematics learning, which emphasizes critical and problem-solving skills leading to critical, creative, lateral, and systemic thinking abilities.