The rifles like others have mentioned are just better for killin deer than any slug gun. That said can you afford to get him a rifle and a scattergun? If not I would recommend an 870 with both barrels. Just always felt it was a waist to have a rifle that you can use for 2 weeks a year and the other 50 weeks the kid cant hunt.
Might be a better move to get him a scatter gun he can kill small game with, get to know the gun, and find a slug it will shoot well. dont put him on a cut corn field but in the brush where shots will be close and the kid has an honest chance of putting some meat on the ground.
Thats how I came up and I killed a ton of chit with my single shot, including deer. I too wanted a rifle but my gramps recommended the shotgun road and it was by far the right choice for me.
