All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Claiming the promotional discount from the student who is behind in the payments isn`t permissible in Sharia. This is because the contract was concluded based on the agreed amount between the club and the student where the latter is liable to make payments and where the discount is offered as part of the bargaining process and to encourage students to join the club. In fact, demanding the amount of discount is a form of Riba (Usury/interest), which is the addition over the original amount of the debt offered against delaying the payments.
Promotional discounts offered by the learning club to students are permissible whereby both parties of the contract must adhere to the stipulations made therein: The club must offer the service and the student must pay the agreed price.
In conclusion, the club is entitled to the agreed price without any addition. Both parties can agree on the original amount without discount where the student who makes payments on time is relieved from a portion of the agreed price and this is considered a promise made by the club to the students who make payments on time. And Allah the Almighty knows best.