When teaching about function and solving equations, get them to think of a function as a production line, with numbers going in and the function doing something to them, and numbers coming out. A fun activity is to get the students to roleplay a production line, with each student performing some operation to a number (e.g. one student might add 2 to it, another might divide it by 5). Then pretend that there are some numbers that have gone through the production line, but were "wrong" or "faulty", so we need to go backwards through the production line and undo everything, to see if the mistake was just putting the wrong number through. This reinforces the fact that to solve an equation, you need to think about what has happened to the independent variable (what goes in), and then undo each of these operations in the reverse order.