To help students increase their confidence it is important to praise them.
How you praise them is just as important.
If you praise them for their intellect or physical ability, what happens if they start to feel they are losing that characteristic?
If you praise them for their effort, the perseverance, the improvement (which is what they actually did) they can do these things even in difficult situations. This sets them up for success in spite of their circumstances.
I researched two books on this subject.
How to NOT talk to your kids Carol Dweck
How to Talk Faber, Mazlish
I also tell my students to NEVER EVER GIVE UP! It's a motto I'm using this year.
The Texans (football team) won a game in the last 2 minutes of the game. The next day I asked my students - What did the Texans do to win the game? They all rolled their eyes and said the motto. At least they said it!