Subjects and verbs must agree in number. This is the cornerstone rule that forms the background of the concept. The dog growls when he is angry. The dogs growl when they are angry. Don’t get confused by the words that come between the subject and verb
This is a great chart for different grammar students may come upon when writing or editing/revising. (Makes a great anchor chart as well). I picked this chart because it is clear cut, easy to read, and would catch students' eyes if I were to color it up.