I used it on two kids. They now both score on standardized tests as reading far in advance of their grade level. This leads to difficulties wherein much of the material available at their level of technical proficiency does not match with either their maturity levels or with their specific interests.

Neither of them actually finished all 100 lessons. At some point, they both preferred moving on to actual books rather than doing the remaining lessons. So a little boring for the student as well, apparently.