If it's an after-school group, why is the school allowing their agenda to interfere during school hours?
The school and the Marxist group share the same agenda.
Lowell is different from traditional public schools as it operates on a modular schedule that is similar to how colleges operate. While some students may be in class, others have those mods off to do homework, study, meet with teachers, and meet with school clubs. Thus, the school clubs can schedule activities during school hours, and invite teachers who may want to bring their classes(hence, optional assembly).