Gather five to 10 pictures from magazines or printed from the computer. These pictures needs to be similar enough that a first-grader could recognize their connection. For example, collect pictures of apples, oranges, watermelons, grapefruit and strawberries to categorize fruit. Replicate this process with whatever type of pictures you decide to find.
Tape the pictures to the poster board in a collage.
Show your class the poster board, and open a discussion about what the pictures all have in common. Using either a notepad and pen/pencil or your classroom's dry erase board and dry erase marker, make note of your first-graders' answers.
Ask you class to give you one word or short phrase to describe all the pictures and what they have in common. Direct the discussion toward the topic you feel, as a teacher, best describes the group of pictures.
Talk about topics. Explain that a topic is the general category for a group of similar items. Further explain to your class that the similarities they mentioned are general topics for those pictures.
Create a title for the group of pictures with your class. Explain how the topic categorizes a group of objects and a title gives them a name. Asking the first-graders to come up with a title for this group of pictures. Give them examples of titles such as, "Fruits in a Bowl" or "Pictures of Fruit."
Display the poster board in the classroom for future reference, as the skill of defining topics, organizing objects and creating and following titles is helpful. Refer back to the poster or its lesson in the future to solidify the idea.