CLMM is based on the idea that specific programs for rehabilitation of offenders have differential effects dependent on offender subgroups and intervention modes. The CLMM hypothesizes certain outcomes given the interaction between individuals at various stages of personality development and their environments. Persons are hypothesized to vary on a dimension called conceptual level (CL), a continuum of conceptual complexity, interpersonal maturity, and self-other understanding. Although CL is considered a continuum, stages or types have been formulated. A Stage-A person is characterized as cognitively concrete and egocentric. A Stage-B individual is intermediate in cognitive complexity and norm-oriented. A person at the higher Stage C is perceived as cognitively complex and interpersonally mature. A substantial proportion of youthful offenders are at the lower stages of development. The CLMM hypothesizes the low CL persons benefit most from high structure, while high CL persons benefit more from low structure, or are less affected by variations in structure. Preliminary studies suggest three tentative conclusions. First, delinquent or maladjusted youth can be reliably classified into CL stages. Second, these youth vary in CL, but they are more likely to be in the lower stages than youth of similar ages in educational settings. And third, lower CL delinquent youth differ in predictable ways from higher CL delinquent youth on behavioral and personality measures. Tables and a list of references are included.