Here's a fun activity for improving word knowledge.
1) Choose a challenge word and give the kids the letters for this word all jumbled up. I used letter stamps but you could use any form as long as they can be moved around.
2) Have your kids try to come up with as many words as they can using the letters provided. Have them write them day. Each time they do this exercise they could try and come up with more words.
3) If you have more than one child, have them compare their lists.
4) See if they can come up with the challenge word. This is the original word that uses all of the letters. Mine was monster.