Your second grader is developing a strong sense of belonging, belief that he is capable and his contributions are valuable. At this age, his self esteem will go through many ups and downs. Hence, it’s a huge responsibility on you to nurture his self esteem carefully.
What you need to do
Watching what you say is very important. Remarks like," You are so lazy" will make him feel labeled as lazy. On the contrary, you can say, " If you finish your homework on time, you will have time for outdoor play". Once he finishes his work, appreciate him for prioritizing work and valuing time. Another way to ensure he develops pride and self-respect, is to provide unconditional love to him irrespective of his strengths, temperaments, weaknesses. Don't compare him with his siblings or classmates. If you value him for what he is, it's more likely he will value himself too.
If he makes mistakes, rather than pointing them, it will be better for him to figure out what caused the mistake and how to avoid repeating them. For instance, if he missed the bus as he got late getting dressed, let the incident make him realize what he can do differently next time, so that he does not miss the bus.
Give him undivided attention and listen to what he has to say. This will make him feel that his opinions do matter and he will feel good about himself.