Relationship duration represents another key determinant of effectiveness. For example, in a reanalysis of the BBBS CBM program, Jean Grossman and Jean Rhodes found that positive effects on youth outcomes became progressively stronger as relationships persisted for longer periods of time. Relative to controls, youth whose relationships terminated within a year appeared to derive the fewest benefits, and those in short matches (i.e., terminating within the first 3-6 months) actually suffered declines in reported levels of feelings of self-worth and perceived scholastic competence. For youth who were in matches that lasted more than a year, however, positive effects were evident on levels of self-worth, perceived social acceptance and scholastic competence, parental relationship quality, school value, and levels of both drug and alcohol use. Likewise, other research has shown that mentoring relationship duration is predictive of youth’s ability to achieve goals, and natural relationships that endure for multiple years have the strongest effects.