Positive, specific praise is such a motivator.
When teaching handwriting I used to ask my kiddies to do their very best and, at the end of the handwriting session, to circle their best letter or word. They always found the best, on their own , and I merely confirmed it.
Here’s an excellent article on Bright Side where they describe the effect of using a green pen to highlight the child’s best work, rather than use a red pen to mark their mistakes, and how this leads to a child’s happiness.
Focus on your child’s best. Be specific. Integrate this approach in all areas of schooling and parenting. Positive comments such as, “You made your bed so neatly,” or “I love the way you packed away all your toys in their boxes,” or “Gosh, you washed these glasses so well!” will make your children (and this applies to others too) feel that their efforts are noticed and appreciated. They love it and it motivates them to keep doing their best.
This is especially important when a child struggles and is despondent. Find just something positive and focus on that.