Personalized Happy 100th Day Of School Long Sleeve T-Shirt. Happy 100th day of school Long Sleeve T-Shirt - Black is a great fun way to celebrate this school year milestone with a class party. Pre-shrunk 100% cotton 6.1 ounce long sleeve t-shirt. Double-needle stitched neckline and sleeves. Quarter turned. Shoulder-to-shoulder taping. Adult: S, M, L, XL, 2XL, 3XL