I have been taking an ASL (American Sign Language) class in college and one of my projects was to read various chapters out of a book titled 'For Hearing People Only' which answers questions that hearing people have about Deaf culture. One of the questions was on if signing should be something that should be mandated and the chapter talks about how kids should be required to learn the manual alphabet as well as numbers in K-1st. At first I disagreed with this but then after reading the article I had a change of view.
One of the points that this article brings up is it helps fine motor development as well as manual dexterity. I know for my kids this isn't a huge deal but for many kids with sensory issues or who are on the autism spectrum or even then ADHD they can struggle in these areas. It can be taught to children and it can be something that is fun as well as educational as you pass secret messages to one another as well as communicate in areas in which it is supposed to be quiet.
Another thing that came to mind with my son is because we've hit 1st grade many times due to a poor pencil grip his hands tire fairly easy. Being homeschooled I do allow him sometimes the ability to tell me the answers and I will write them such as in math. I am looking forward to teaching him his manual alphabet to do spelling as well as his manual numbers to do math problems. This gives him the ability to fidget and move and yet work on his school work in a non-traditional way
There are many sites you can go to learn how to do the manual alphabet but not all sites teach the manual alphabet correctly. The site below teaches the correct fingerspelling for even the letter 'f' which is usually done in books and other publications incorrectly.