In this study, the impact of the wheelchair on the self-efficacy for the user was investigated with a newly developed scale called R-MATE (Retrospective Measurement on Assistive Technology Outcome). Using R-MATE, the user is asked to produce the time course line of their self-efficacy retrospectively. The line has the value of 100 as the baseline for the time period with no disability. The user is also asked to state their life events along the produced line, that relate to their disabilities and the introduction of Assistive Technology (AT). There were thirteen participants in this study. All the participants had Duchenne Muscular Dystrophy (DMD) and used a powered wheelchair daily when this study was conducted. The result showed two significant drops in the time course of the self-efficacy of each user. It is interesting to note, that the use of a powered wheelchair increased self-efficacy, when compared to its former value during the time without DMD and that the user did not begin using a new wheelchair until they had lost much of their self-efficacy.