If a slippery slope is an idea or course of action which will lead to something unacceptable, wrong, or disastrous (that's from NOAD), then one way to make an "opposite" of that would be to describe a course of action that will lead to something fruitful or prosperous – such as an education.
With that in mind, one expression you could use is toehold: a relatively insignificant position from which further progress may be made.
UPDATE: I was composing my answer as you were composing your update – now it seems like my answer is off-the-mark. Still, I'll leave it here as an example of why it's so important to clarify what you are asking about, particularly when it comes to "opposite" questions, since words and expressions can have more than one opposite (the opposite of light can be dark or heavy, for example).