Graph proportional relationships, interpreting the unit rate as the slope of the graph. Compare two different proportional relationships represented in different ways. For example, compare a distance-time graph to a distance-time equation to determine which of two moving objects has greater speed.
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.