Discovery learning involves trying things out, experimenting and getting it wrong. This is how young children learn. Instruction is a far less efficient way to do this, as anyone who has spent any time with 3-7 year olds can tell you. You can tell children things as many times as you want. You can read a perfectly designed script that explains phonics. And then that child will turn around and say 'How can I become a caterpillar?' and your speech is halted in its tracks. What we say to children and what they learn are very different things. Children learn through discovery and play. If we don't understand that, then we do them a grave disservice.