Your preschooler is probably already showing an enthusiasm for learning. Most preschool age children are very observant, ask many questions, and are eager to read and write. You might be seeing physical evidence of this when you find drawings on the wall or scribbling in the novel you have been reading! Take advantage of this opportunity to teach your child to recognize the upper and lower case letters of the alphabet. If you have taught him the traditional ABC song and he has memorized it, this is a good sign that he is ready to progress to recognition and writing.
Toddlers and preschoolers are visual learners, so keeping pictures of upper and lower case letters displayed will help your child learn to differentiate them. You can show him flash cards, or hang an alphabet poster on the wall. Using sticky notes is fun for children. Write the upper and lower case letters on separate notes. Stick the uppercase letters on the wall or a table and let your child place the matching lower case letter over them. Sticky notes will come off the wall a lot easier than magic marker!
Preschoolers also learn by using manipulatives, which are tangible items that help explain a concept. Foam and plastic letters are available at teacher supply or dollar stores. Mix them up and let your child sort the upper and lower case letters on the floor.
You can teach your youngster many skills just by reading aloud to him. Show him the cover of the book and point out the words that have upper case letters. Pause while reading and get him to point to an uppercase letter. After reading, go back to a few pages and ask him to find a lowercase "s" or "a" or any other targeted letter. If you do this frequently, your child will probably point out letters everywhere he sees them around the house or in the store.
Writing the alphabet is another method for teaching the difference between upper and lower case letters. Your preschooler probably would not be too interested in a dull worksheet, but there are other ways to write. For example, pour some salt on a tray covered with two pieces of construction paper that are different colors. Let your child write the upper case letter on one piece of paper and the lower case one on the other. If you don't mind a mess, let your child write letters in cool whip that you put in a plate. Who cares if he gets it all over himself and you? For a preschooler, that is part of the fun.
Your preschooler probably enjoys playing games, so choose a few that are fun and educational. Starfall (Link in Resources) is an online early learning site with many reading games. On "Let's Get Ready to Read,", your child can click on any letter and the upper and lower case versions are displayed while a child's voice says the name and the sound of the letter.