Music technology can provide unique opportunities to allow access to music making for those with complex needs in special educational needs (SEN) settings. Whilst there is a growing trend of research in this area, technology has been shown to face a variety of issues leading to underuse in this context. This paper reviews issues raised in literature and in practice for the use of music technology in SEN settings. The paper then reviews existing principles and frameworks for designing digital musical instruments (DMIs.) The reviews of literature and current frameworks are then used to inform a set of design considerations for instruments for users with complex needs, and in SEN settings. 18 design considerations are presented with connections to literature and practice. An implementation example including future work is presented, and finally a conclusion is then offered.