Spirometry provides a quantitative measure of lung function and its use is recommended as an adjunct to enhance pediatric respiratory healthcare in many clinical practice guidelines. However, there is limited evidence confirming the benefits (or otherwise) of using spirometry from either clinician or patient perspectives. This systematic review aimed to determine the impact of spirometry on change in clinical decision making and patient-reported outcome measures. We searched PubMed, Embase, Cochrane Central Register of Controlled Trials, www.clinicaltrials.gov, and World Health Organization International Clinical Trials Registry Platform, from inception to July 2021. We included randomized controlled trials (RCTs) comparing the use versus non-use of spirometry during standard clinical review in children aged <18 years with respiratory problems in clinics. We used Cochrane methodology. The search identified 3475 articles; 8 full-text articles were reviewed but only 1 study fulfilled the inclusion criteria. The single study involved two cluster RCTs of spirometry for children with asthma in general practice. The included study did not find any significant intergroup difference at the 12-month follow-up for asthma-related quality-of-life and clinical endpoints. However, the findings were limited by methodological weaknesses and high risks of bias. With a paucity of data, the clinical benefits of spirometry remain unclear. Thus, there is a clear need for RCTs that provide high-quality evidence to support the routine use of spirometry in children with suspected or known lung disease. Pending the availability of better evidence, we recommend that clinicians adhere to the current clinical practice recommendations.