The purpose of this research was to determine the effect of formative testing and self-directed learning on mathematics learning outcomes. The research was conducted at an elementary school in central Jakarta during the 2014/2015 school year. Seventy-two fourth-grade students who were selected using random sampling participated in this study. Data were obtained through testing and were analyzed using a two-line analysis of variance (ANOVA) according to the treatment design and level of self-directed learning. The results showed that (1) mathematics learning outcomes differ between students who are given formative essay tests and those who are given formative multiple choice tests; (2) there is an interaction effect between formative testing and self-directed learning on mathematics learning outcomes; (3) students with high levels of self-directed learning have better learning outcomes when given formative essay tests than when given formative multiple choice tests; and (4) students with low levels of self-directed learning show no difference in mathematics learning outcomes based on whether they are given formative essay tests or multiple choice tests.