Hi luxy.
Comprehension is a vital part of all communication. By assesing comprehension can give us information on developmental progress and any possible hearing difficulties. Depending on the age of your client base, comprehension is ushally assessed by asking the client to carry out a series of tasks. With clients such as stroke victims a speech therapist would ask them to point to the floor, or touch their nose. This would then be followed witha two part command such as close your eyes and wave your hand. This gives us and insight into the area of impairment, be it aphasia, dysphasia etc, it helps to loacte the area of the brain which has been damaged.
With children this follows much the same pattern. When assessing a childs comprehensions simple tasks will be admisistered such as "put dolly on the chair". It helps to determine what stage the child is as and highlight any hearing difficulties. It is especially important to assess comprehension in children as this can also affect expression. If a child is not able to hear words correctly, this can then affact the way they produce speech sounds.
Hope this helps a little, im not sure what area you are in but this is generally the way we assess comprehension and underatnding. Of course it can go into much more detail, but this is just an initial assessment. x