School systems frequently provide instruction and classes for individuals who are behind in particular subjects. You want to determine if a reading program is effective for children with reading...

School systems frequently provide instruction and classes for individuals who are behind in particular subjects. You want to determine if a reading program is effective for children with reading difficulties, so you test all second-grade children on reading ability. The children who score below 30 on your test of reading ability are required to participate in the reading program. After these children have been in the reading program for a time, you again test all the second-grade children on reading ability. You find that the children given the program improved more than would be expected and conclude that it indicates that the program was effective.