Assimilation is the process of taking in new information and fitting it into a preconceived notion about objects or the world.

Accomodation means adjusting to new experience or objects by revising the old plan to fit the new information.

"Schema (pl. schemata) is a simple mental image or pattern of action, a form of organizing information that a person uses to interpret the things she sees, hears, smells and touches." (The Piaget Primer, p. 17)

In modern cognitive sciences, we more often use the term mental|cognitive|internal "representations" (C-representations = comprehension|understanding representations; P-representations = production|action representations)