Clue: Member of large class in brief learning, infants and maybe elders? (6)
Answer: INSECT
Explanation: Definition: Member of large class
Insects form the largest class in the animal kingdom 
*thanks to NeilW – insects are in "brie**F LEA**rning"; in "inf**ANT**s"; in "may**BE E**lders"*
 
~~not at all sure on the parsing, but I'll have a guess:~~
 ~~maybe **INST**ruction="brief learning", with **EC**=Early Childhood="infants and maybe elders?" inside~~