"There's a lot of talk these days about giving children self-esteem. It's not something you can give; it's something they have to build."
Self-esteem and confidence are built from hard work and success. The overly simplistic model of IBL teaching is that we pitch (some) problem just outside the grasp of students, and through hard work, support, and guidance, students succeed. Repeat. Repeat. Repeat...
Success breeds confidence like no other. Good teaching practice can support fruitful struggle that then leads to new knowledge (for students), ways of thinking, habits of mind, and the oft-elusive quality of confidence.