My child guesses at words when he's reading. How can I help him get over this habit?

Practice makes perfect! But what if your child guesses every time he comes to a word he doesn't know? He just looks at the picture and says the first thing that comes to his mind! To fix this, first be sure that your child really knows the letter sounds. He needs the tools to be able to decode words in order to give up guessing and to begin to read words quickly and on sight. Once he knows the sounds, you've got to get him to use them as his first line of offense, rather than guessing as a first choice.
One way to help overcome the guessing habit is to help bring it to his attention in a fun way. Put up a finger every time the child guesses at a word. If he can read a whole page without having one whole hand up, he wins or gets a point or an M&M! Place 5 chips or markers near the page the child is reading. Move them or take one each time the child guesses. The goal is to read the whole page without taking a single guess. Sounding words out one at a time will slow down the reading, but reading speed will improve as the child practices the quick decoding of words. Just remember that learning to read takes lots and lots of practice!