Lots of good discussion. First of all, Yahoo! Dictionary's 大辞泉 has this:

[用法] 目的・目標――「目的（目標）に向かって着実に進む」のように、めざすものの意では相通じて用いられる。◇「目的」は、「目標」に比べ抽象的で長期にわたる目あてであり、内容に重点を置いて使う。「人生の目的を立身出世に置く」◇「目標」は、目ざす地点・数値・数量などに重点があり、「目標は前方三〇〇〇メートルの丘の上」「今週の売り上げ目標」のようにより具体的である。

That still leaves something to be desired, though. I think what cinefil-san has said about being a 手段 or not is important here. I think you can look at the two like this:

The 目的 is the 的 - it's the bull's eye that you have in your sights. But if you break that journey to the bull's eye down, there are smaller goals to make along the way. Perhaps it's extremely windy, so you need to aim to the right of the bull's eye. That point somewhere along the way between you and the bull's eye where the arrow strays just enough to the right that the wind takes it back to the bull's eye is a 目標. And if you're precise, you can set several of them. These are 標識 along the way that lead you to the 的.

出発点➝目標➝目標➝目的（到着点）.

The problem is that with a change of perspective, what seemed to be an end goal can suddenly become a stepping stone along the way to a larger goal, and vice versa. If you narrow your perspective, suddenly that point at which the arrow begins to change its path back toward the target becomes the larger goal, with several smaller stepping stones to reach it along the way. And in the same fashion, if you zoom out then perhaps that bull's eye is just a stepping stone in your journey to improve your archery. And perhaps you are practicing archery to find discipline or inner peace.

Being able to identify the parts of a motor doesn't sound like an end goal to me. It sounds like knowledge that you would pick up along the way to achieving a larger goal like being able to repair that motor. If your perspective is this single lesson alone, then perhaps you might look at this as the 目的, but a teacher needs a broader perspective than that - units, courses.

By the way, my 日本国語大辞典 also has this for 目標:

②学習指導要領などで、目的よりも一段と具体化されためあてをいう語。

So there is of course the issue of domain and where the words are being used. Lastly, I just thought I would mention that when I was an ALT at an elementary school, all of my lesson plans used ねらい.