I’m adding “Writing Help” from Time For Kids to The Best Websites For K-12 Writing Instruction/Reinforcement. I particularly like the model essays that each section includes.

You might also be interested in my other “The Best…” lists related to writing:

The Best Places Where Students Can Write Online
The Best Sites For Grammar Practice
Not “The Best,” But “A List” Of Mindmapping, Flow Chart Tools, & Graphic Organizers

Future “The Best…” lists I’m preparing on writing include:

The Best Sites For Learning How To Writing Biographical Essays

The Best Sites For Learning How To Write Response To Literature Essays

The Best Sites For Learning How to Write Persuasive Essays

The Best Sites For Learning How to Write Problem/Solution Essays