An educator compares differences in academic performance on a standardized assessment among 15 students at the beginning of the class year and again at the end of the class year. They find that the mean difference in academic performance (beginning –

end of class year) was −100 points, with the estimated standard error for difference scores being 40. If the null hypothesis states that academic performance will not differ

(µD = 0), then what is the decision for this test for a two-tailed test at a .05 level of significance?

a. Fail to reject the null hypothesis; children did not show improvement from the beginning to the end of the class year.

b. Reject the null hypothesis; children showed significantly worse performance from the beginning to the end of the class year.

c. Reject the null hypothesis; children showed significantly improved performance from the beginning to the end of the class year.