Below are some useful sites which can help children and teenagers learning about English language and grammar. They cover literature, poetry (reading and writing), and grammar. Some include word games that will appeal to some children.
Age recommendations vary enormously depending on the ability and interest of the child. Children interested in words may like to read my language pages about UK/US word differences, or the homonyms pages which list words that sound the same in British English but have different meanings. If you want a very basic introduction to grammar and parts of speech, see the page introducing grammar.
BBC revisewise - brief descriptions, interactive activies and exercises in reading, writing and grammar. Officially for ages 4-11 (primary) but levels vary between activities.
Reading matters - a useful selection of book reviews for children (about age 8-11) and teenagers. Information about authors and suggestions for further reading too.
Giggle poetry - a light-hearted introduction to humorous poetry, including a set of 'poetry class' pages with good explanations about how to write various types of poem, from limericks to raps. Suitable for any age.
CY magazine - a site designed to inspire and entertain children aged around 7-12 with news, articles, puzzles, competitions and reviews. Registration (free) required to enter some parts of the site.
Poetry 4 Kids - rhyming dictionary, poetry games, poetry writing contests, and how to write a humorous poem. For any age.
Ongoing tales - poetry - well-known and lesser-known poems to read and enjoy. Mainly intended for primary age (4-11)
Ongoing tales - fairy stories - all the old favourites fairy stories and some which are not so well-known
Fun Brain - word games to help children appreciate word differences. For primary age, depending on ability.
Young Writers' Club - a site where children (mostly aged 7-15) can join a free online club submit, and submit their writing for publication. Plenty to read, also book reviews and suggested activities.
Learn 4 Good - actually intended for people learning English as a second language, but with a useful set of grammar rules and explanations for various forms of speech. For teenagers (and adults!)
Blue Book of Grammar - a useful set of rules and examples for some of the trickier grammar questions. Mainly for teenagers.
Guide to Grammar and Style - for older teenagers who know the basic rules and want to learn ways of improving their writing style. A miscellany of rules, explanations, comments and suggestions.
Humorous Grammar Rules - for those who basically know how English is conventionally written, this is an amusing list of rules, each one breaking itself.
Ten Steps to Writing an Essay - American in style, but for anyone wanting to write formal essays, this site explains the basic principles as taught in US schools. Suitable for about age 8 and older.
How to write an essay - a much more extensive explanation, really intended for university students in the UK but appropriate to teenagers interested in this topic.
Absolute Write - excellent resource for freelance writers, with market listings, articles and interviews. Mostly adult writers, but this would be suitable for interested teenagers too.
English National Curriculum - for anyone wanting to know how English works in British schools, here is the outline National Curriculum for English for each 'key stage' level.
Art and craft - English - Geography - History - Languages - Maths - Music - RE - Science