what are the methods of teaching / learning / memorising "spellings" to children of class III?

Answer 1

Repitition is important. Let the children say the word then spell it out aloud. Remember to break the words down in syllables. I find that children learn better when they listen. In fact it is said that audible retention has more impact than visual retention. If you can get cassettes with the words on them that would be great.
Also let the children use the words in everyday simple sentences. This should aid greatly with the learning process.

Answer 2

That's a pretty broad question. It depends on the word.