Most learning in the workplace occurs while pursuing working rather than learning goals. The studies at hand aimed to identify task characteristics that foster learning in the workplace. Task characteristics are supposed to exert a major effect on the learning potential. However, the fact that learning is more often than not a rather unconscious by-product of working poses methodological challenges because respondents might not be capable of accurately recalling daily work experiences. Diaries were applied in order to bring measurement closer to the processes. Three diary studies were conducted in the field of office work within vocational education and training, with trainees requested to record particular work tasks several times a day. Each diary record, i.e., each work task, required a rating of ten standardized items relating to task characteristics including the perceived learning potential of the present task. Eighteen trainees aiming to become retail salespersons recorded 488 work tasks, 10 trainees aiming to become bank clerks recorded 1,113 work tasks, and 20 trainees aiming to become industrial clerks recorded 573 work tasks. The aim of these studies was to explain the variance in the perceived learning potentials from further task characteristics using regression analyses. The extent of the explained variance ranged from 46.6% in study 1 to 77.8% in study 3. Interestingness, novelty, assistance from others, and feedback turned out to be the best predictors, whereas scope of action even showed negative influences. Practical implications for workplace learning as well as methodological recommendations for using diary methods in the workplace are discussed.