The short answer: use waterproof stick-on vinyl labels for gear (drink bottles, lunch boxes, books, pencils) and iron-on labels for anything that goes through the wash (uniforms, hats, jumpers).
Stick-on labels: for everything hard
Vinyl stick-on name labels are the workhorse of the school bag. They are waterproof, and they go in the dishwasher on the top shelf away from a high-temperature setting — drink bottles and lunch boxes get washed daily, and paper labels give up in a week. Small labels (20 × 50mm) fit drink bottles, pencil cases and book covers; pencil labels suit pencils and cutlery; larger labels are easier for teachers to read across a classroom. Apply to a clean, dry, grease-free surface and leave the label 24–48 hours to cure before its first wash.
Iron-on labels: for everything soft
School jumpers migrate. Iron-on clothing labels put your child’s name inside collars and waistbands permanently — applied with a household iron in under half a minute each. Wash the garment in cold water, which is what the labels are made for. Order them at the same time as your stick-ons so everything matches.
How many do you need?
Count the things, not the child — the sizes and quantities guide walks the book list and the uniform list. As a rule of thumb, one to two packs of stick-ons plus one pack of iron-ons covers a year, and giving each child their own colour makes sorting the washing glance-work.
What makes a label survive a school year?
Three things: the material (waterproof vinyl, rather than paper, for anything that gets wet), the print (UV-stable inks that do not fade in the sun), and the corners — rounded corners resist peeling, and sharp corners are where labels die. All Oz Labels stick-ons are printed and die-cut in Australia with rounded corners as standard.
Boarding school is a different question
Boarding houses use commercial laundry, usually with hot water, and iron-on labels are made for a cold wash. For a boarder, use sew-on labels — see iron-on vs sew-on vs clothing stickers for the full comparison.