If you have a child with asthma, you probably know that their symptoms can vary for many reasons. One way to help assess your child’s asthma is a lung function test.  A lung function test (spirometry) evaluates how well your lungs work – how much air you can breathe in, how much air you can blow out and how quickly you can do it.  The test consists of breathing into a mouthpiece that is hooked up to a computer.