In the study, it was aimed to investigate the leniency/severity, bias and halo effect of the raters which were used in the scoring of the diagnostic tree prepared by the teacher candidates with the many-facet Rasch model. The research study group constitutes 24 teacher candidates who are taking measurement and evaluation lesson from the students of the faculty of teaching department of classroom teaching in a state university. Teacher candidates in the study team have formed two groups between themselves. Each group developed a diagnostic tree related with their field. Diagnostic trees prepared by teacher candidates were scored by a faculty member in the direction of the same criteria and 12 peers selected from each group. The effects of scoring were determined and the data were analyzed with the many-facet Rasch model. In the study, it was reached to the results that some raters rated severely on some criteria and groups than expected, and some raters showed halo effects on an individual-level.