Personalized That Was Pretty Cool 100 Days Of School T-Shirt. Whether it's a special event at school or a casual day out, our "That Was Pretty Cool 100 Days Of School" design is a must-have for your little one. It's a great way to commemorate this important milestone and create lasting memories. Get yours today and let your child shine on their 100th day of school! 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.