Learn French: Vu que l'effectif augmente, la charge de travail est lourde. - Seeing that the class size is increasing, the workload is heavy.

Even though it ends in que, vu que introduces an objective, observable fact ("seeing that" or "given that"). Because you are stating a reality rather than an opinion or a doubt, it requires the indicative mood.

L'effectif is translated as "the class size" here. Can it be used in other contexts?

Yes, un effectif refers to the total number of people in any specific group. In a school setting, it means "class size" or "enrollment." In a business, it typically translates to "staff," "workforce," or "headcount."

Is la charge de travail the standard expression for "workload"?

Yes! Une charge literally means a "load" or "burden." Combining it with de travail creates the standard, most natural way to say "workload" in both academic and professional contexts.

Could we put vu que in the middle of this sentence?

Absolutely. Just like in English, you can flip the clauses: La charge de travail est lourde vu que l'effectif augmente. Both structures are completely natural in everyday French.