A subject verb is created when the act of doing something becomes the subject of a sentence. For example, although swimming is a verb, in the statement, "Swimming is fun," the act of swimming is now the subject of the sentence.
Yes, the sentence has a singular subject (one tragic effect), and a singular verb (massive flooding.)
In this statement, the verb "make" signifies the action of parents assuming the role or position of being the best teachers for their children. It implies that parents have a significant impact on their children's education and development.