Following a history of the SWIP plan launched in 1977, the article describes the methodology used in a 1984 survey of four prisons with different types of SWIP programs. The survey revealed certain factors which appeared to influence survival of SWIP schemes: stable regimes, evidence of the probation department's integration in the prison, and the model of SWIP operative in the prison. Analyses of four SWIP models showed the lowest lapse rate for the one where prison officers were attached to prison probation departments full-time for a continuous period varying from 3 months to over 2 years. Assessment of SWIP effectiveness found an overall impression that it did contribute to a much more effective prison regime. Key factors influencing effectiveness were time being made available for prison officers to practice and develop their skills and the commitment of those directly involved being matched by that of key probation and prison personnel. Other shared work projects are discussed. Three references.