Clue: Rebellious kid regularly hiding bath sponge (6)
Answer: LOOFAH
Explanation: Definition: sponge
A charade of LOOF, a reversal ('rebellious'; as a reversal indicator, it might be better in a down light – uprising. In an across clue, it is more likely an anagrind, in this case for an indirect anagram) of FOOL ('kid') plus AH ('regularly hiding b**A**t**H' **– i.e. the B and T are hidden). Of course, a biologist will claim that sponges and loofahs belong to different kingdoms, but their skeletons serve similar purposes, and are both called sponges.