Midgley is well known for his efforts to articulate what is known in the academic literature as the developmental perspective in social welfare. This perspective is based on the idea that traditional approaches have tended to separate social welfare from economic considerations and, in particular, have done little to enhance people's abilities to participate effectively in the productive economy. The developmental approach seeks to transcend the remedial and maintenance functions of social welfare by promoting a strengths-based alternative that invests in what Nobel Prize winner Professor Amartya Sen calls 'human capabilities'. In this way, it seeks to promote the productive economic participation of clients and to advocate for social policies and programs that contribute to economic development. Social investment does not reject the need for remedial services but places greater emphasis on strategies that restore those in need to effective functioning and help them to lead productive and fulfilling lives.

Other members of the Social Investment Group include Professor Julian Chow and doctoral student, Will Rainford. The Group is involved both in theoretical and empirical research. Recent theoretical contribitions by Midgley have been published in Social Service Review and in the Handbook of Social Policy. In September 2000, Midgley gave a keynote address on welfare theory, developmentism and assets at a national symposium on asset building organized by Professor Michael Sherraden at the Center for Social Development at Washington University in St. Louis. The symposium was funded by the Ford Foundation. Midgley collaborates with Sherraden whose research into assets has not only attracted international attention but has resulted in the enactment of federal and state legislation creating numerous asset development programs. Midgley's theoretical work underpins the assets approach.