Capping education allowances when international school fees rise 9% a year?

Education is now the second largest line in our assignment budget after housing. We are a food and beverage company with 64 long-term assignees, 39 of whom have school-age children, mostly in Shanghai, Dubai, Lagos and Mexico City.

Policy is actual tuition at an approved international school, uncapped. Average cost per child is USD 31,000 and the top is USD 52,000. Fees have risen by around 9% a year for three years, and the choice of school varies a lot between families in the same city.

Has anyone introduced a cap or an employee contribution for people already on assignment, and how did it land?