The court ruled Friday that an arbitrator doesn't have have the right to make up new rules around class size outside of the provincial School Act.
In 2009, an arbitrator decided that as long as a class did not exceed 33 students, then only the opinions of a principal or superintendent mattered when determining if the size and composition was appropriate.
The rule under the School Act capped class sizes above Grade 4 at 30 students, "unless the principal consults with the teacher and the principal and superintendent form the opinion the class is appropriate for student learning."
B.C. Teachers' Federation president Susan Lambert said Friday's legal victory is only a small step toward solving the real problem facing the education system.
"The key to getting smaller class sizes and the key to providing services to students with special needs is funding. We have to have adequate funding and at this point we don't have that," she said.
In June, B.C. teachers voted to ratify a new tentative contract agreement between their union and the B.C. Public School Employers' Association.
Lambert noted that the union felt compelled to reach a deal in order to avoid potential fines and the threat of punitive legislation.