Why are we looking at somebody for motivation? We are all human beings, we are not Gods. Even teachers are human beings too. Bad mood/good mood/hot-temper/good-temper/patience or not can't predict right?
Look at what the school materials are.
Let the child get used to all these changes as long as the materials are benefit to the child.
The child must have independency, positive attitude in facing challenges ahead, confidence, self-discipline, longer attention span, concentration skill, inter-personal skill. Together with good materials, wow.......
That is an excuse if failing the subject and start blaming that the teacher is no good. If the teacher is no good, why other students in the same class can pass?