Homework is a common instructional practice that is used to motivate students, develop students' studying skills and habits, inform parents about student learning, and increase student achievement. Homework provides an opportunity for students to revisit daily topics, and improve students' understanding of math concepts and problem-solving skills, helps students learn from their mistakes, and prepare for tests. One of the primary goals of this study was to find the trends of homework frequency. This study used TIMSS [Trends in International Mathematics and Science Study] 2003, 2007, 2011, and 2015 data for Singapore, United States, Slovenia, and Turkey. The study used hierarchical multiple regression analyses to examine the relationship between homework frequency and student achievement in fourth- and eighth-grade mathematics in Slovenia, Singapore, Turkey, and US. The study also sought optimal homework frequencies in those countries. The study found that homework frequency significantly effects student achievement in 8th grade but not in 4th grade. The study also found that trend of the assigning homework from 2003 to 2015 is negative both in 4th and 8th grades in all selected countries, except in Turkey.