Extremely small pet peeve: "for all intensive purposes"

The phrase is "intents and purposes," not "intensive purposes." It doesn't both me particularly, not as much as the inability to get reign and rein straight. It even charms me a little, because "intensive" is nearly always spelled right, so clearly the person does care about their words! But, indeed, it's "for all intents and purposes," which I think makes a little more sense than "for all intensive purposes," since the point is that the purposes need not be intensive!

And now, back to grading, wherein not only does "intensive purposes" not come up, but students often use the wrong pronoun for each other and drop "not" more often than you'd imagine.