This study was conducted to determine: (1) if there were a significant difference in the effectiveness of vocational counselors as compared with regular counselors and vocational teachers in an on-the-job guidance task, and (2) the relationship of counselor background characteristics to effectiveness ratings of the counselors. In each of the 25 cooperating school districts, 10 sophomore students were selected at random, administered the Ohio Vocational Interest Survey, and assigned to a vocational counselor, regular counselor, or vocational teacher who conducted a one-hour session with each student, discussing individual test results and career planning. Following the interview, students completed the Counseling Evaluation Inventory (CEI), which served as the counseling-effectiveness criterion instrument. Personal background and characteristics data were collected from each counselor prior to the counseling interviews. No significant differences were found among the three groups of counselors when counselor-effectiveness data were analyzed by a one-way analysis of variance-blocked test. Correlational analysis of CEI scores and background data revealed 11 background and personal characteristic variables that were significantly correlated with counselor effectiveness ratings. Significant correlations were obtained in the areas of personal information, work experience, teaching background, and personal attitudes. (SB)