This study describes the development and validation of the Homan-Hewitt Readability Formul~ This formula estimates the readability level of single-sentence test items. Its initial development is based on the assumption that differences in readability level will affect item difficulty. The validation of the formula is achieved by (a) estimating the readability levels of sets of test items predicted to be written at 2nd-through 8th-grade levels; (b) administering the tests to 782 students in grades 2 through 5; (3) using the class means as the unit of analyses and subjecting the data to a two-factor repeated measures ANOVA. Significant differences were found on class mean performance scores across the levels of readability. These results indicated that a relationship exists between students' reading grade levels and their responses to test items written at higher readability levels.