Why Should We Conduct An Aptitude Test?

An aptitude test measures the ability of an individual to learn, and gives some indication of their mental abilities.  By measuring aptitude in educational environments, a certain level of management can be performed to ensure that children aren't faced with situations where they will be overwhelmed.  The tests are supposed to be used as tools to aid in providing the best possible learning experience for each student.
Children sometimes develop in different stages, and a child may become more capable as he or she grows older.  The results of aptitude testing are not intended to be applied as permanent criteria for any individual.  That's one of the reasons that educational systems keep implementing different forms of standardized testing.  Someone may be more capable of learning when they are eight than they were when they were five.
The general purpose is to at least have some information to work with in the beginning that will be beneficial to the child's development.