The purpose of this mixed-method designed research was to study factors affecting the development of the 21st century’s foreign language learning potentialities of higher secondary school students in terms of the schools’ policies, problems in the policy administration, the schools’ curriculum administration, problems in the schools’ administration, the teachers’ roles and class management, problems in class management, the students’ roles, and the knowledge they can apply in their lives. The target group was at Muangphon pittayakom School, including the Deputy Director of Academic Affairs, foreign language teachers, and senior high school students. Three sets of five-level closed-ended and open-ended questionnaires based on Likert’s and unstructured questions were used to collect the data from the target group. The director of the school answered the questionnaire and unstructured questions by himself. He revealed that the school followed the policies of the Ministry of Education at three levels: (1) the highest level in terms of encouraging the students to love being Thai, to be able to work with others, and to live with others; (2) a high level in terms of ethics and analytical thinking; (3) a moderate level in terms of creative thinking and technology. He specified that his administrative problems concerned the improvement of the curriculum, the lack of teachers, and the teachers’ workloads. The problems related to the foreign language management were the students’ lack of leadership and confidence in speaking English, the lack of instructional media, some difficult text, and the students’ weak background of English. Two foreign language teachers answered the questionnaire and unstructured questions concerning the teaching management. They stated they realized their roles as teachers at the highest level in all aspects except analyzing individual student, setting goals for the students, and selecting appropriate instructional media, which were at a moderate level. For their teaching, they strictly followed all indicators of the curriculum. Their only problem was that the students did not realize the importance and benefit of English, for they live far away from the city. The students realized their roles at the highest level, and they said they could apply what they had studied at the highest level, too. However, they requested the school for more computers, books in foreign languages and in Thai. In addition, they wanted the teachers to create pleasant learning atmosphere, let them watch some foreign movies, display their outstanding work, speak the language studied in class, invite native speakers to class sometimes, and put on foreign language plays.