This study uses a process of organising the teaching of biology for students following a STEM education orientation and examines the impact of this teaching process on the development of students' problem-solving and creative competences. Research and organize the implementation of three STEM lesson plans for 382 selected 11th-grade students in 3 schools in Hanoi, Vietnam, in 2023. To assess the development of the problem-solving and creativity competence of students, the research is based on the structure of problem-solving and creativity competence, including 4 skills: problem identification (KN1); proposing and selecting solutions (KN2); planning, implementation, and evaluation of solutions (KN3); and report presentation (KN4). Assessing these four skills will show the level of students' problem-solving and creative competence. This study documents the positive relationship between STEM-oriented biology teaching and the development of students' problem-solving and creativity competences. Specifically, teaching STEM-oriented subjects increases students' problem-solving and creativity competences. The interesting thing is that classes with a small number of students are more effective in developing problem-solving and creative competence. Research has suggested that in classrooms with fewer students, teachers have more opportunities to interact with each student. The research results are of interest and beneficial to educational policymakers, schools, and teachers in trying to develop students' learning competencies, especially core competencies like problem solving and creativity.