Cognitive tests are designed to measure a learner’s innate ability to learn. It gives us information about the learner’s abilities compared to others his/her age in various areas (e.g. verbal ability, fluid reasoning, perceptual reasoning, processing speed, working memory). Scores on the cognitive test predict how well a learner can learn new information. However, we have to remember that these scores are not deterministic. A high score does not always mean good school performance, and a low score does not always mean failure. Other factors such as behaviour, interest, and motivation also have to be considered.
While cognitive tests measure learning abilities, achievement tests measure how much the learner has acquired. They focus on the academic skills learned (e.g. reading, writing, mathematics), and give us an indication of how well the learner is doing as compared to others his/her age or grade level. Students would have taken achievement tests in school. The PSLE is an example of an achievement test our children sit for.
To give an example, achievement tests might test how well a student can do on academic math tasks (e.g. problem sums, memory of formulae). Cognitive tests, on the other hand, would test for generalised problem-solving and logical thinking skills, which are typically not explicitly taught in the classroom.