For over 30 years, Peter MacIntyre shaped and innovated the way(s) in which second language acquisition (SLA) researchers investigate individual differences (IDs) of language learners. His work significantly contributed to the sophistication of conceptual models for learner ID variables such as willingness-to-communicate, anxiety, and enjoyment, advanced theoretical perspectives and approaches, and pioneered methodological innovations, such as the idiodynamic method. The purpose of the present study is to take Peter's pioneering vision and innovative spirit as starting points and to apply multiple aspects of his work to the empirical investigation of language teacher IDs. Specifically, the study takes a longitudinal approach and examines the (dynamic) change trajectories in language teachers' anxiety and enjoyment in two different classroom scenarios over a period of nine weeks. Quantitative online survey data was collected from 93 language teachers and analyzed via individual growth curve modeling, using gender and experience level as time-invariant, and coping potential as time-varying covariates. Results indicate unique change trajectories and inter-individual differences for both emotions across both classroom scenarios. Findings also suggest that time-varying, rather than time-invariant variables, consistently explained substantive amounts of variance and variability in language teachers' emotion trajectories. Directions for future research and practical implications are discussed.