Personalized Happy 100th Days Of School T-Shirt. The Happy 100th Days Of School design features vibrant colors and playful elements that capture the excitement of reaching this important milestone. It's a great way to show off your school spirit and commemorate the hard work and dedication that goes into 100 days of learning. Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.