This paper explores a stepwise learning approach based on a system's decomp
osition into functional subsystems. Two case studies are examined: a visual
ly guided robot that learns to track a maneuvering object, and a robot that
learns to use the information from a force sensor in order to put a peg in
to a hole. These two applications show the features and advantages of the p
roposed approach: i) the subsystems naturally arise as functional component
s of the hardware and software; ii) these subsystems are building blocks of
the robot behavior and can be combined in several ways for performing vari
ous tasks; iii) this decomposition makes it easier to check the performance
s and detect the cause of a malfunction; iv) only those subsystems for whic
h a satisfactory solution is not available need to be learned; v) the strat
egy proposed for coordinating the optimization of all subsystems ensures an
improvement at the task-level; vi) the overall system's behavior is signif
icantly improved by the stepwise learning approach.