Quick Note: I came up with this WAAAAAAAY before Avatar: The Last Airbender and Sky High. Any similarities are a result of coincidence and not that of foresight or planning.

Phew, now that that's out of the way...

CLAN: Book 6: Hemaphobia

A 16 year old boy, Will, is in his home when his stove catches fire. His single mother is killed in the fire. By the time the firemen and police and ambulences get there, the fire is put out and a huge body of water is flooding the streets.
Will is taken by the headmaster of a school for these "manipulators". This school (sort of like the High school in Sky High and the Watchtower in Justice League) is in a constant mid-atmospheric orbit above Earth.
In this school there are Clans. Made of manipulators, these Clans consist of Water, Fire, Water, Earth, Air, and a mysterious new sect made of Shape-shifters. Advanced students learn to harness their rare "secondary element" (i.e. a Fire student learns Air as well and learns Lightning Manipulation.

Fire + Air= Lightning
Earth + Air= Gravity
Air + Water= Ice
Fire + Water= Acid
Fire+ Earth= Lava/ Magma
Earth+ Water= Mud)

In this school Will makes many friends who help him through the strange and wonderful, weird and fantastical, dangerous and magical world of The Clans.

This series consists of 70+ books of about 50-150 pages. A few chapters at a time (much like comic books but no pictures.)

Book 1- Master of Elements
Book 2- New Boy
Book 3- Girl of Water
Book 4- On Ice
Book 5- Attack
Book 6- Hemaphobia