You're a bit stingy with the context here, but if this is a text by Piaget it may have something to do with language acquisition.

If you need to translate this into another language, you may well be able to retain the English term.

For understanding, go back to the meaning of bootstrap. Since many boots have a tall section above the foot, the maker of the boot sews a strong strip of leather to the back of the boot, at the top where you put your foot into the boot. It is most difficult to fit one's heel into the boot, right. So, as you pull the boot on, you have a strategically placed extra gripping point at the back, at the top, above the heel. If someone else is helping you with your boot, this strip also helps.
In learning something, the learner needs "aids". The rest of the passage probably suggests some of these aids...prior knowledge, specific vocabulary, images, hands on work and so forth.

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Note added at 7 hrs 59 mins (2005-01-22 13:13:26 GMT)
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Are you trying to understand the meaning or are you preparing to translate into another language? Not knowing your purpose in asking makes answering difficult!
There\'s another educational jargon concept which comes to mind: scaffolding. That means building toward a final concept by basing new material and thinking on earlier knowledge.

Maybe this might help you;
bootstrap: to promote or develop by individual initiative and effort with a minimum of outside assistance - often used reflexively

...design to function independently of outside direction: capable of using one internal function or process to control another( operation to load a computer )...

...carried out with minimum resources or advantages;self-reliant