In this study we used a factor of curves model (FCM) to examine the co-development of the subdomains of boredom in practical English language classes in an online setting (BPELC) over time in four phases of an online L2 course to explore the covariance of the initial level and slope of the sub-domains, as well as to check to what extent the variation in these subdomains can be accounted by the underpinning global factor of BPELC. Data were collected from 412 adult EFL learners on four temporal occasions via the "Boredom in Practical English Classes--Revised scale," created by Pawlak et al. (2020a). Analysis was conducted by Mplus in three stages. Findings revealed a statically significant decrease over time in both subdomains. Also, a negative covariance was uncovered between the initial level and the growth level of each subdomain. Moreover, the covariances between the initial and growth levels of both subdomains were moderately high. Finally, the variances of the initial and growth levels of each of the subdomains were accounted for to a great extent by the underpinning global factor of BPELC. The results are interpreted in view of the underlying theories of boredom.