This study examines whether ten weeks of direct instruction of affixes with online systems can improve learners' knowledge of affixes by using Affix Master 10 (AM10), a collection of online self-study materials developed by the current researchers. The aim of AM10 is to let students comprehensively learn 30 prefixes and 31 suffixes. The two research questions are (1) whether systematic instruction of affixes using the online program improves learners' knowledge of affixes (prefixes and suffixes), and (2) whether systematic instruction of affixes using the online program improves learners' knowledge of affixes without direct instruction as well as those with direct instruction. The results found that after learning with AM10, the affix knowledge statistically significantly increased. Furthermore, it seemed to contribute to the learning of the affix system itself, which was evidenced by the gain in knowledge of untaught affixes. [For the complete volume, "Intelligent CALL, Granular Systems and Learner Data: Short Papers from EUROCALL 2022 (30th, Reykjavik, Iceland, August 17-19, 2022)," see ED624779.]