Trainee characteristics play a role in the learning, retention, and transfer of skills and factual material. We now identify three additional factors that account for differences in individual learning processes: differing rates of trainee progress, interactions between attributes and treatment, and the training of adults and older workers. People learn at different rates. Some people progress more quickly than others, and individual learners may even progress at different rates during the same training program.

A useful way to show rates of learning is by drawing learning curves. A learning curve is plotted on a graph with learning proficiency indicated vertically on the y-axis and elapsed time indicated horizontally on the x-axis. When implementing a new HRD program, learning curves can be used as baselines for communicating expectations of progress to future trainees and trainers and as aids in scheduling and planning future sessions. Some methods of training may be better suited to certain types of people. Research on attribute-treatment interactions (ATI) has sought to develop training systems that can be adapted to differences between individual learners.

Researchers such as Malcolm Knowles note that many instructional methods and principles of learning have been developed with and for children, and they argue that teaching adults requires a different set of techniques. Pedagogy is the term traditionally used for instructional methodology, and it has most often emphasized educating children and teenagers through high school. Knowles proposes an adult-oriented approach to learning called andragogy. A pedagogical approach emphasizes more one-way, downward communication, whereas an andragogical approach uses more two-way communication.

A pedagogical approach is more likely to focus on rules, subject matter and a rigid format, whereas an andragogical approach is more likely to be flexible, open, and developmental. Recent research suggests some differences between older and younger adults in certain learning situations.