I know at my school what is learnt in one semester is usually not needed in the second semester. So say in maths they learn half the topics in the first semester and then the other half of the topics in the second semester. I think it is the same in other subjects such as english and science. And end of year exams and assignments are usually based on the semester rather than the whole year.
But as suggested, speak to the principal and see what would be done to help with the transition and the year following. GL