This article is very interesting and attractive for intervention studies, but several issues need to be clarified before the model is implemented to understand the effect of intervention. They are listed in the followings:
1) Since all students at the pre-test stage were labeled in the same class, is it necessary to conduct interventions on a specific group of students?
2) The intraclass correlations were estimated in the basis of the multilevel 1-parameter logistic model, but a multidimensional 2PL IRT model was used in subsequent analyses.
3) The sample size is considered small for model evaluations.
4) The time difference was short in the present study, but at most of time the assumption of measurement invariance is very strong in longitudinal studies, particularly when a study is conducted over years.