Interpret the equation y = mx + b as defining a linear function, whose graph is a straight line; give examples of functions that are not linear. For example, the function A = s<sup>2</sup> giving the area of a square as a function of its side length is not linear because its graph contains the points (1,1), (2,4) and (3,9), which are not on a straight line.
What should we do if we encounter an equation that - gasp! -- does not have y isolated? Kids learn how to manipulate the equation into slope-intercept form, without using that vocabulary... yet.
Is the kid "on the line" or not? :)
Get kids to figure out whether a given point is a solution to a linear function by defining what a solution is -- namely, an ordered pair that makes the function true.
Are you smarter than an 8th grader? Based on the popular TV series, it's kids vs. a teacher (it could be the music teacher, the English teacher, whomever) in a battle over prowess in 8th grade mathematics.