A teacher gives a reading skills test to a third-grade class of n = 25 at the beginning of the school year. To evaluate the changes that occur during the year, students are tested again at the end of the year. Their test scores showed an average improvement of M_D = 12.7 points with s² = 100.

a. Are the results sufficient to conclude that there is significant improvement? Use a one-tailed test with = .01.

b. Construct a 90% confidence interval for the mean difference to describe the size of the improvement.