Talk with your son's first-grade teacher and explain what his kindergarten year was like. If you have any samples of his work or his uncompleted workbooks, show them to the teacher. She needs to understand why your son is having such difficulty with the expectations this year.
Also, talk with the teacher about setting up a positive reward system to encourage your son's work completion. Ask her to let you know on a daily basis (this could be as simple as a smiley face or a check mark in his planner) how his day was with regard to completion of written work, then follow up at home. A good day can earn an extra bedtime story or a walk around the block just with you. Two or three good days in a week can earn having a friend over to play on the weekend. You can increase the amount of good work required for a reward as he improves.
Give your son opportunities to improve his handwriting and his fine motor skills at home. Make sure that he has lots of paper and fun markers and pencils to practice his letters, scissors (even ones that cut patterns), Legos, puzzles, blocks, and clay. Give him a cookie sheet coated in pudding so he can practice writing his letters with his fingers. He can do the same with a pan of sand or cornmeal. If you feel that your son has a delay in this area, you can have him evaluated by an occupational therapist to determine if work with a therapist may help him.
Try to work with the teacher to help your son improve these skills this year. The expectations of second-grade teachers with regard to written work are even higher, as are those in third grade, fourth grade, and so on.