There are sturdier boxes but you cannot beat the price and convenience of these for moving boxes. They are small enough that you can be sure not to make it too heavy when filling with books - a perennial challenge for homeschoolers and other book lovers.
This is the best way to pack a house to move. They aren't too big and not too overwhelming to unload. Since they are all the same size they stack easily. The lid protects belongings from dust and dirt. We just needed a few bigger boxes for large things.