Teaching 800 students

I have just finished teaching for the week and have taught more than 800 students. One of the English teachers left so I am now teaching one lesson a week to 18 different classes in Primary 4, 5 and 6. Before this week I was teaching nine classes twice a week I am now teaching 18 classes once a week and will continue to do so for the next month until the exams.
I have been teaching Primary 5 and 6 therefore it was easy to teach the three Primary 5 classes I had not previously taught. Although teaching Primary 4 is a new experience. There seems to be a large gap between Primary 4 and 5 and its difficult to know how to structure the class.
In every class there is about 45 students therefore I am now teaching more than 800 students a week. I already struggled to remember five students names. I have no hope of remembering any of the students names.
Teaching the three year levels also means I have to write three exams. It could be interesting to write an exam for the Primary 4's having only taught them one lesson.