Sentence:  Of startling significance , too , <WSD>is</WSD> the assertion that it was possible to carry out this program with only a 6 percent attrition rate as compared with a rate of 59 percent reported for a comparable group of families who were receiving help in traditionally operated child guidance services . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)