A nurse is instructing a school-age child who has asthma about the use of a peak expiratory flow meter. Which of the following instructions should the nurse include in the teaching?

The correct answer is C: Blow into the meter as hard and quickly as possible. This instruction is important because the peak expiratory flow meter measures the maximum speed of air breathed out. Blowing hard and quickly ensures an accurate reading of the peak flow rate, which is vital for monitoring asthma. Maintaining a semi-Fowler's position (A) is not necessary for using the peak flow meter. Placing the tongue on the mouthpiece (B) may obstruct airflow and lead to inaccurate results. Recording the average of the readings (D) is not as important as obtaining an accurate peak flow reading.