Disappointed test result

I had been teaching for one month plus n completed topic one which was suppose to finish last two weeks ago. The topic was delay due to students going to National day practice. Today i gave my Year 9A class test which was suppose to be last Saturday but half of the class did not turn up so i give them the test today. Still two students absent today, which i did not know is it due to medical leave or some other reason. I was quite disappointed when marking the test paper (simple calculation students also cannot calculate), is it due to my lesson not clear or ......... I did took out three questions from the test paper and gave them revise before hand. I found out that some students cannot do the three questions i gave for revision. This prove that some students did not revise for their test. The whole class fail badly. What happen to the students nowadays? Teacher already told them test today and yet they still do not revise. There are lots of repeaters in Year 11 this year in my school. I had one student entering my Year 11SS2. I had him as my first lesson yesterday. That boy was so far so good. I hope he wont disturb my class when teaching. I do not understand why the admin put him into normal class instead of in repeater class........