There are 25 million displaced children worldwide, and those receiving schooling are often educated in overcrowded classrooms. Montessori is a child-centred educational method that provides an alternative model to traditional educational approaches. In this model, students are able to direct their own learning and develop at their own pace, working with materials rather than in supervised groups or with direct teacher instruction. Because most children are working alone, teachers have more time to work one-on-one with children even when student-teacher ratios are quite large. This gives teachers increased opportunity to tailor their teaching to the specific needs and strengths of each student. We conducted an evaluation of Montessori classroom conversion for displaced students on the Thai-Myanmar border. We administered the Ages and Stages Questionnaire (ASQ) to 66 children before and after classroom conversion and across treatment and control classroom conditions. We then conducted difference in difference testing. All domains showed meaningful improvements in ASQ scores, with the Montessori students gaining 18 points relative to the traditional students (p = 0.33). However, only the personal-social domain of the ASQ was statistically significant (8.8 point gain for the Montessori students relative to the control, p < 0.05) in our underpowered sample.