Hence the 3-dimensional chart for determining adjective ending -- it depends on gender, case, and the word preceding it (i.e., definite article, indefinite, or nothing). Although I found a chart on this page that "reduces" it to a four-branch flow chart:
http://www.nthuleen.com/teach/grammar/adjektivendungenexpl.h...
But in principle I agree with you. We need a bit of book learning to go with the "just start speaking" approach.