Long-term evaluations of student performance are important to show whether Multilingual Education (MLE) students are making real progress, as well as to show what changes are needed to make MLE programs more successful. The purpose of this paper is to describe a six-year study of MLE students in Southern Thailand. .In 2007, the Research Institute for Languages and Cultures of Asia, Mahidol University (RILCA-MU) initiated the Patani Malay-Thai Bi/multilingual Research Project in four schools in Southern Thailand. In 2011, the Yala Rajabhat University (YRU) staff began biannual student evaluations of both the experimental (MLE) schools and the "normal" Thai-only comparison schools, when the first cohort of students began primary grade 1. YRU followed these students' performances until 2016 when they completed primary grade 6. The learning achievement for students in the experimental (MLE) schools was found to be significantly higher than that of students in the comparison schools at the level of 0.01, except in grade 6. The number of students who met the basic educational criteria was greater for the MLE schools than the comparison schools. MLE was found to be very helpful for low and mid-level performing student. Finally, scores on the critical thinking skills assessment of the MLE students were greater than the comparison school students. Thus, this six-year research project has clearly shown that MLE can help to solve the problems of teaching and learning in Thailand's three southern border provinces. This approach to long-term evaluations can be helpful to projects in other countries also.