Planning plays an instrumental role in prominent self-regulation theories (e.g., action regulation, control, goal setting), yet as a scientific community we know little about how people carry out their learning plans. Using an experimental field study, we implemented a repeated-measures intervention requiring trainees to create a plan for when, where, and how much time they intended to devote to training before each of 4 online modules and examined the conditions under which the planning intervention improved learning and reduced attrition. Trainees benefited from the planning intervention when it was paired with another intervention--prompting self-regulation--targeting self-regulatory processes that occur subsequent to planning (e.g., monitoring, concentration, learning strategies). Trainees' learning performance was highest and attrition lowest when they received both interventions. The planning intervention was also advantageous for enhancing learning and reducing attrition when trainees followed through on the amount of time that they planned to devote to training. Finally, the relationship between planned study time, time on task, and learning performance was cyclical. Planned study time had a positive effect on time on task, which, in turn, had a positive effect on learning performance. However, trainees planned to devote less time to training following higher rather than lower learning performance. The current study contributes to our theoretical understanding of self-regulated learning by researching one of the most overlooked components of the process--planning--and examining the conditions under which establishing a learning plan enhances training outcomes. (Contains 3 tables, 1 footnote, and 5 figures.)