Is a function increasing or decreasing?
The advent of the graphing calculator has helped students and teachers understand and explain this material much more easily and clearly. The best example is to use a right side up parabola and ask the student verbally. When shown the Power Rule of Calculus at the same time, the student can then support his/her answer (or change it accordingly!!). The next task is show the contrast between the parabolic and the cubic so that the student can see that y = x^3 is ALWAYS increasing!!
Then we can revisit the idea of a line and how it has a constant rate of change -- all of these concepts can be well demonstrated by using the xy table on the graphing calculator.