The COVID-19 pandemic has prompted an unprecedented shift from face-to-face to online learning. Considering the impact of this transition, the researchers developed a scale measuring the stress levels of 319 junior high school students. Based on the evaluation of experts, the item content validity index (I-CVI) proved the validity of each item. From the original 32, 20 items were retained after conducting exploratory factor analysis (EFA). A new clustering was derived from the results, namely: (1) physical health, (2) task management, (3) valuing, and (4) relating to oneself and others. The final 20-item scale was proven to have internal consistency among items with Cronbach’s alpha of 0.923. The results of measurement invariance (MI) tests indicate that the newly developed four-factor stress scale in the context of online learning measure the same underlying constructs across sex, grade level, and age groups. Consequently, the differences in stress levels among the groups were also determined.