Evidence is here brought together suggesting that educational and other psychological tests are appreciably dependent not only on the abilities that they are supposed to measure, but on the form and material of the tests and their items, sets and attitudes in the testees, and various conditions of testing. The factors that emerge when tests are inter-correlated represent to some extent these formal characteristics rather than desired intellectual functions. In particular this applies to current educational tests which, for sound educational reasons, avoid simpler, more factual, items and prefer complex comprehension-type or problem items. While tests of the same objectives employing different forms tend to give discrepant results (e.g., essay and new-type), tests in the same form which are aimed at different school subjects or different intellectual functions inter-correlate very highly. This detracts from their validity, especially in counseling or differentiating abilities along different lines. For many purposes the simpler tests show superior validity, and it is doubtful how far the more complex ones do bring in the 'higher' intellectual functions at which they are aimed.