This is the title of a short story I recommend.
Author: Jeanne Willis
Illustrator: Tony Ross
First published by Andersen Press Ltd., 2005, UK
Spanish version: La promesa del renacuajo,
published by RBA, Barcelona, 2007
Translator: José Morán Orti
About the author:
Jeanne Willis wrote her first book when she was five years old and hasn't stopped writing since. She has now written over eighty titles, including picture books, novels and television scripts. She has also won numerous awards, including the Children's Book Award, The Sheffield Children's Book Award and the Silver Smarties Prize. Her teen novel, Naked Without a Flat, was shortlisted for the Whitbread Award in 2004. She writes with her pet rat keeping her company and often takes inspiration from dreams and interesting conversations with strangers.
About the story:
The creators of "I Hate School" bring their usual sense of wit and wisdom to this hilarious, coming-of-metamorphosis story about two of nature's star-crossed lovers: a tadpole and a caterpillar.
There´s a post with interesting comments here