Spearman"s two-factor theory states that intelligence consists of general factor and specific task- related factors. Sternberg"s triarchic theory is example of information processing approach. emphasizes importance of adaptive behaviour in a natural environment. Gardner"s theory emphasizes categories of aptitudes and skills (both physical and cognitive) Binet developed a series of tests, stanford-binet scale. used to identify children that need special attention. Binet and simon developed the concept of norms with which to compare a particular individual. Wechsler developed intelligence test for adults (wais) and children (wisc) Their validity is difficult to assess because there is no single criterion of intelligence. Intelligence tests are used to identify special student so they can benefit from appropriate educational programs. Intelligence test may be abused if teachers expect little from students labelled as unintelligent . fail to encourage them to achieve the most. Variability in intellectual abilities is produced by three sources: 1) environmental variability, 2) genetic variability, 3) interaction between the two.