Decorate the ceiling with hanging paper dinosaurs. Laminate and hole punch the dinosaurs, then tie a string through the hole so you can attach the dinos to the ceiling with a paper clip. This only works if your classroom has a drop ceiling with tiles you can easily lift. Otherwise, you can tape the dinosaurs to the ceiling using strong tape. Check with administration to determine what is permissible to put on the ceiling.
Line bulletin boards with dinosaur-theme borders. Many teacher resource stores have decorative bulletin board borders with dinosaurs on them. If you can't find one with dinosaurs, choose a grass-themed border.
Place large cardboard cut-outs of well-known dinosaurs in various places in the classroom. Put a friendly-looking dinosaur near the entrance to greet students coming in. Place a not-too-scary looking T. rex in an empty corner of the room. You also can hang dinosaur posters on empty wall spaces around the room.
Display dinosaur books prominently on the bookshelf. Encourage students to read books about dinosaurs during quiet or free time. Some dinosaur books recommended for school-age children are: "National Geographic Kids Ultimate Dinopedia: The Most Complete Dinosaur Reference Ever" by Don Lessom, which has extensive information about everything dinosaur in a kid-friendly format; and "The Magic Tree House: Dinosaurs Before Dark" by Mary Pope Osborne, about two kids who are magically transported to the time when dinosaurs roamed the earth.
Create a dinosaur discovery center. Designate an area of the room where kids can play with toy dinosaurs during free time and dig through a sand pit for dinosaur fossils. They can also create dinosaur-related art. Hang fun facts about dinosaurs in the area, and place dinosaur footprints leading from the classroom door to the dinosaur center.