Motivation is critical to student success in learning environments. However, changes in situation-specific motivation over time are rarely explored among online learners. Drawing from the Situated Expectancy Theory (SEVT), in the current study, I examined changes in situational task-specific task value and cost over the short term and tested the impact of these changes on achievement. I collected task value and cost over four time points from 68 students in an upper-division online Educational Psychology course. Grades on two discussion posts and one exam represented academic performance. I used multiple analytic techniques, scarcely used in the literature, to measure change across time, including task value-cost switching and group and individual-level task value-cost intensity. Group-level intensity analyses revealed task value and cost stability across most time point comparisons. However, individual-level analysis demonstrated variability in task value and cost across comparisons. There was no evidence of task value or cost switching. One significant increase in cost across tasks predicted academic performance in the subsequent assessment. The study highlights the importance of using various techniques to explore motivational changes among online learners and demonstrates the applicability of SEVT in online learning environments.