What is the ruling of Islamic law on a teacher's participation in educational strikes that cause students to miss lessons?

There is no objection to striking to improve the workers' conditions. A strike is a means that takes the ruling of its objective: if it is for the achievement of an obligatory matter, then it is obligatory; and if it is for the achievement of a forbidden matter, then it is forbidden. Thus, if the demands are permissible and the workers have a right to them, there is no harm in participating, and no responsibility for missed classes. However, if the demands are illegitimate, participation is not permissible unless non-participation would lead to harm for the teacher or students.