preparatory (adj.)

"serving to prepare the way for something to follow," early 15c., preparatori, from Late Latin praeparatorius, from Latin praeparatus, past participle of praeparare "make ready beforehand" (see prepare).

Earlier in same sense was preparative (c. 1400). The word was applied by 1822 in the United Kingdom to junior schools in which pupils are "prepared" for a higher school.