The debate on single-gender education has been ongoing for a long time. It has always been involved with several aspects on how it would affect human society including people in the society and human behaviors. In addition, the debate on benefits between single-gender education and coeducation has also taken place in the society today, especially in Thailand. It can be noticed that this issue has become an important issue in Thailand and the tendency of single-gender education to take place in Thailand is apparently less than coeducation. Nevertheless, adolescents who graduate from single-gender schools tend to benefit from their schools rather than those who graduate from coeducational schools. Thus, single-gender education has more positive effects on adolescents in Thai society in the 21st century