Young scientist Fabiola Gerpott is exploring the effects of actual and perceived age diversity in organisations. As the workforce in many countries grows older, more and more companies are recognising the value of initiatives to promote ‘lifelong learning’. Older workers are increasingly given the opportunity to participate in the training and development programmes organised by human resources departments. But because older employees have been mostly excluded from such activities in the past, studies of the effective age composition of training groups are rare. In my research, I find that perceived – rather than actual – age diversity influences both knowledge sharing and learning outcomes in training programmes. I also highlight the importance of a positive learning climate to maximise the effectiveness of personnel development.Within the field of diversity research, the findings of previous studies on the effectiveness of age-diverse work teams are inconclusive. On the one hand, it is argued that age-diverse groups may benefit from the different perspectives of employees with varying generational backgrounds and experience. On the other hand, age-diverse groups can suffer from greater conflict and failure to communicate effectively. To shed light on these contradictory results in the context of organisational development, I conducted a survey of 189 participants in one-day training programmes at a company. Each of the participants belonged to one of 16 training groups, which varied in their age composition, ranging from almost no variation to an age range of up to 29 years. Participants filled in a questionnaire before and after the training programme. They provided their age and indicated how similar they felt the training group was with regard to the age of its members. In addition, they answered a range of questions on group climate, their own and other participants’ knowledge sharing as well as learning outcomes. My statistical analysis of the survey data shows that objective age diversity influences neither the amount of knowledge sharing nor individual learning outcomes. But perceived age diversity – that is, the subjective rating of participants – has a slightly negative effect on both outcome measures. Group climate (the feeling that information could be shared openly and group members appreciated the contributions of employees from all age groups) turns out to be the most important factor. It has a strongly positive effect on individual knowledge sharing and learning outcomes. These findings suggest that objective age diversity is neither an asset nor a threat for the effectiveness of firms’ training programmes. In contrast, individual’s subjective perceptions of age diversity and training group climate significantly influence the effectiveness of training. Thus, companies should focus on creating a positive learning climate and reducing the salience of age diversity to enhance the outcomes of their training programmes.