His major contribution was in the field of readability. From the beginning of the 20th century, the assessment of the grade level of texts for different grades of readers was a central concern of reading research. It was well known that without correctly graded texts, readers would not improve their reading skill. There were over 1,000 published studies on this topic. Klare's contribution to that effort came both in his critical reviews of the studies and his participation in original research.