Aarushi S.

Hi,
I hope you and your family are safe and doing well.
I would suggest one thing that helped me stay focused and sit for long hours than I used to when I was in school. I used to learn through different eye-catching videos. Your son is in 1st standard and probably would be around 5/6 years old. At that age, children most likely get attracted to other unique visuals (such as cartoons). So, you can try once to see if there is any difference or not to make him study using videos or pictures. It is also scientifically proven that people tend to remember more things they see visually. 
I won't recommend too much screen time as it also harms the child's eyes and may want him only to learn that way.
But I would recommend using different techniques to teach him. E.g., while teaching him numbers or addition/ subtraction - you could use crayons to depict how if you take out one crayon from 7 crayons, the result will be six crayons - well, just an example). This way, he also remains intact in learning new things and may also show interest.

Thank you, and stay safe!