This study investigated the professional traits of mathematics teachers that affected mathematical achievement for fourth-graders in the TIMSS 2015 study, including teaching experience, degree of educational qualification, teacher specialization, and amount of professional development, all broken down further by gender. This investigation compared TIMSS 2015 results of students in four countries (Singapore, Hong Kong, Japan, and Saudi Arabia) and used a causal-comparative design with data available through the IEA website. The findings indicated that the traits of professional development, specialization, educational qualification, and teaching experience among mathematics teachers were found to have various levels of impact on the achievement of fourth-grade students in the participating countries, as will be stated in the discussion of the results.