Praise be to Allah, The Lord of Worlds.
Since the bus driver is at the parents' disposal and is committed to transporting their children to and from school then he is entitled to the monthly wage in full, and students` absence isn`t valid ground for nullifying the Ijarah (Hiring) contract or deducting any portion of the driver`s wage. This is unless the driver abstains from this task or fails to perform it where any excuse on his part is considered unacceptable no matter what the case may be. The reason for this is that the authority entitled to decide when students are to go to school or not is the Ministry of Education and not the bus driver. Thus, a portion of his wage should be deducted in return for the days students had missed school because of him.
His transporting students to and from school is considered Ijarah Forward. In this kind of Ijarah, the worker (Bus driver) complies with perfroming the agreed upon service, regardless of the type of vehicle used. Rather, it suffices that he transports the students to and from school. In addition, there is nothing wrong with offering this service to many clients (students) at the same time, and this worker, according to jurists, is called Ajeer Mushtarak. According to jurists, Ajeer Mushtarak is a worker who offers his services to many and thus may be contracted by many clients, but Ajeer Khaas is a hired-worker who is contracted by one party to perform a specific task in a pre-defined amount of time. Kindly refer to "Rawdat At-Talibin, 5/228." By the Shafie jurist Annawawi.
Since Ijarah contract rests on fulfilling a benefit, which is transporting students to and from school, it isn`t rendered annul if that benefit wasn`t actually fulfilled, as stated the Shafie jurists. Annawawi said, "Ijarah contract isn`t annulled by excuses, be it Ijarah Forward or else. For example, leasing a camel for travel, but getting sick, leasing a shop to make crafts and backing off or the tools get burned and the like."{Rawdat Attalibin, 5/239}. And Allah the Almighty knows best.