This review focuses on 16 studies in which the effects of tutoring were measured using student achievement, being limited to studies appearing through 1969. Additional studies that the authors subsequently found are considered to still support the conclusions drawn in this review on the general characteristics of successful tutoring programs and successful tutors; and to support the value of directed, structured tutoring when pupil achievement is the criterion. In six of the studies examined in this review, posttest achievement scores for tutored pupils were found to be, in statistical terms, significantly superior to scores of control groups. However, since these results are frequently not presented as grade equivalent scores, it is considered difficult to assess the effectiveness of tutoring in any educationally significant terms. In two other studies that were "successful," nagging questions about the design and outcome measures had been raised; two additional studies which did not have control groups showed one group of middle school pupils as making reasonable progress in reading, and no gains at all in the second project. In five other projects, there were no statistically significant differences between the pupils in the experimental and control groups. Four studies which reported objective data on the effects of tutoring upon tutors were found to be inconclusive; objective measures of affective changes were either nonexistent or showed no significant differences due to tutoring programs. (RJ)