During an asthma attack, people may have difficulty breathing and may begin to breathe very fast. They may also feel short of breath, even at rest. The child with asthma may need to use the muscles around the chest to help with breathing. Wheezing and coughing are also important signs that can occur during an attack, or even when a child is feeling well. A persistent night-time cough is one common sign of asthma, even in children without other symptoms.

Often a doctor can hear the effects of asthma in a patient's lungs on physical exam. Sometimes, an instrument called a spirometer is used to test a child's breathing in order to help make the diagnosis of asthma.

When an asthmatic patient is having an attack, that person must work harder to move air in and out of the lungs. Patients with asthma can use a home monitor called a 'peak flow meter' to follow their ability to breathe. A loss of peak flow can signal an asthma attack.