Performance, usually in school work, poorer than that predicted from aptitude and/or intelligence testing. ... (12 Dec 1998) ... 
Type: Term Pronunciation: ŭn′dĕr-ă-chēv′mĕnt Definitions: 1. Failure to achieve as well as one's abilities would seem to allow.
[n] - poorer than expected performance (poorer than might have been predicted from intelligence tests)
noun poorer than expected performance (poorer than might have been predicted from intelligence tests)