Is it permissible to save a portion of one's salary in a bank that yields interest to cover future school expenses for children, knowing that this interest will be used solely for schooling?

It is not permissible to save one's salary in an interest-bearing account to secure the future; rather, this is from the whispers of Satan. Money can be invested in trade or deposited in an investment account with reliable Islamic banks. Spending interest (riba) on school fees does not make usury permissible. The true future that must be secured is what comes after this worldly life, and it can only be secured by obeying Allah's commands and avoiding His prohibitions. It is a mistake to secure an uncertain worldly future with something that forfeits happiness in the true afterlife.