You do need to realize that your son has some weak skills, or the school would not have considered him for retention. He probably would like to go to school and would even enjoy his teacher if school were easier for him.
This year, you must work closely with your son's new teacher to ensure that he does not fall behind. Start now by finding out what extra help the school can provide and whether it would be a good idea for your son to have a tutor. If so, it should be someone who can work cooperatively with the teacher.
To reduce the tension at home, set up a definite time when you will work with your son every day for about 20 minutes. If he has homework, make sure he understands the directions and then help him work the first few items to make sure he is on the right track. Also, the tutor or another family member could supervise his homework. Above all else, make sure someone in the family reads to him every day.
Use your son's desire to play to incorporate games in his daily routine that will build his skills. Math skills can be practiced through any board game that requires the throwing of dice. You can take games that have spinners and use dice instead. For vocabulary building, place words he needs to know on cards and spaces on game boards. Use your ingenuity to create more games, and look for games at learning stores.