Indoor air quality (IAQ) in educational facilities is an important factor in student's well-being and academic achievement. Window opening and air infiltration are commonly used as the sole ventilation sources in current educational buildings, which can lead to unhealthy levels of indoor pollutants and energy waste. In this paper, the impact of infiltration and exfiltration on CO2 concentrations was evaluated in three studios at the architecture department in the American University in Cairo by the means of fan pressurization testing and onsite CO2 PPM concentration measurements. The monitoring protocol took place under normal operation schedule in which number of people in the space was recorded along with other parameters such as manual airing status by window opening. Airtightness was then assessed using pressurization test method which was carried out in these classrooms to assess air infiltration caused by envelope leakages. Two sets of linear regression models were developed to estimate CO2 concentration in the space: one for when windows are closed and another when they are opened. The two sets were then compared to understand the effect of airtightness on CO2 concentration. The findings indicated that ventilation cannot rely solely on air infiltration, and that particular controlled ventilation systems should be employed to optimize IAQ while avoiding excessive energy loss.