A Dutch version of the National Intelligence Test has been given each year to 13-14-year-old candidates of the boys' industrial school attached to the Philips works. IQ's in the post-war years average 4 points lower than in pre-war years, presumably as a result of educational setback during the war. Other tests closely related to school training showed more decline from 1944 to 1947 than tests unrelated to schooling, thus supporting the contention that lack of training was responsible. The evidence shows that IQ reflects any conditions which alter the rate of mental development. (PsycINFO Database Record (c) 2006 APA, all rights reserved)