Personalized Happy 100 Days Of School T-Shirt. Whether your child is marking their 100th day at school or you're a teacher looking for a fun way to commemorate this milestone, our 100 Days of School Apparel is the ideal choice. 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.