Girls and boys are participating equally in the senior secondary levels of schooling in Thailand. After major reforms of the science curricula at all levels in the 1970s, about 10% of each age cohort are now studying physics, chemistry and biology in each of the three years of senior high school. The learning in physics of these students has been assessed with practical tests involving manipulative skills and problem solving, theoretical tests of physics knowledge and of source of evidence and an attitude to science test. The girls performed at least as well as the boys in all these measures of learning. In the practical tests, the girls in single-sex schools outperformed both girls and boys in co-educational schools and the boys in single-sex schools.In conjunction with earlier evidence of girls' superior learning achievements in chemistry, these results negate suggestions of biological bases for the widespread under-achievement of girls in the physical sciences elsewhere. Organizational aspects of the secondary curriculum, that encourage girls and boys to continue studying science and then require all three sciences to be studied, seem to be the major factors in these remarkable achievements in physics education.