Private paid tutoring is one of the most common approaches of remedial instruction to improve school performance of poorly performing pupils. The expansion of private tutoring was affirmed in a study with 904 pupils in Luxembourg. 23% of the participants reported that they receive tutoring at present, mainly in the subject matter of Mathematics. Theoretical considerations suggest the effectiveness of private tutoring in promoting school performance by an improvement in cognitive and motivational variables and a higher amount of time spent on task. However, appropriate evaluation studies are lacking. In an empirical study the effectiveness of tutoring is evaluated in a prepost-control-group-design. One group (N=122) received private tutoring over a period of nine months and was compared to a non-tutoring control group (N=122). These results indicate that receiving tutoring leads to a larger improvement in school performance and motivational variables. Directions for further research and practical implications are discussed.