With the advent of information technology, various online homework systems have often been utilized to enhance students' knowledge and skills. Several studies analyzed the effects of web-based homework systems on students' learning through comparing them with paper-pencil homework. However, few studies explored students' homework completion behaviors (e.g., starting early or late to solve homework problems) in online homework settings. To fill the gap, this study examined students' use of the WeBWorK, an online homework system, in three undergraduate mathematics courses and the impact of their usage of the system on their final exam and overall homework grades. The findings revealed that students who made more attempts on solving homework problems displayed considerably higher performance on homework and final exam than their peers having less attempts. Although students starting early to answer homework questions obtained higher homework scores than the late starters, they were unable to reflect their homework performance on the final exam.