You are quite right when you say that boys mature later than girls.  However, if all the basic concepts are established and the fact that he can write his name and read some words, then I do not see why he should not be placed in kindergarten.  There has been no research to my knowledge but I do think that at most you should do what is right for your grandchild.  Ask the present teacher what she thinks about his emotional maturity.  He might even surprise you - they tend to be really into their teacher and sit still for that length of time.  The down side of keeping him back for another year means that all his friends are in a grade above him and he has to make new friends.  Mostly in this instance if he stays - boredom could set in which then has its own set of consequences.  It's a tough call and I wish you everything of the best.

Hi Liz,

I don't know about research, but I have 4 kids (ages 4,5,7, and 10) and they are all different! I have 4 girls but also have many friends with boys and I know that they typically need that extra year to develop more mentally as well as needing that extra time with mom. Our now 7 year old was born Dec. 1, the cut off day to start Kindergarten in our state and when she was 5, she was the youngest in her class. She did fine though, but once it came time to start 1st grade is when it caught up with her and it was just too much for her and she had to repeat kindergarten. This was the best thing that could have happened to her. She breezed through it and then was SO ready and able to handle the first grade.
She is now at the top of her class and I can guarantee you, if you work with your child at home, with worksheets like they offer here and do a lot of reading your child will also benefit from that extra year and be so much more able to handle the stresses of school (kindergarten is VERY demanding these days, not just coloring and singing, they WORK HARD all day!) as well as exceeding academically! Don't let people pressure you into thinking he HAS to start at 5 or he will be behind! This is just not true and all my girlfriends with boys who all waited until they were 6 can tell you the same. Some kids just are ready (like my other 3 could have started at age 4 LOL) and others just aren't...trust me NO ONE will know when he is a grown, WELL ADJUSTED man, that he was 6 and not 5 when he started kindergarten! Don't lose sight of what's important in the long run and that is the well being of your child!

I chose to start my children in kindergarten at age 6. They have not had any negative effects from this. When they started they were ready. My only advice to you is that if you start him late, work with him at home daily. Educate yourself about state standards for your state for kindergarten. It is not all playtime and naps these days.

Our son needed the extra year to mature.  We felt it was a great decision for him.  It is always a good idea to let them 'cook' another year!

The problem, though, is that most people don't really care about what is best for their children, only what is most convenient for them.  We started our son in Kindergarten at age 6 and found most of his classmates were 4 going on 5.  Now in the middle of 1st grade he is bored and has very little socially in common with his classmates who are mostly a year and half younger.  We are looking to bump him up to 3rd grade next year because of this.  Watch out for this problem, and put him into a school with multiple classes per grade, that way you know the school will be able to segregate the children by age and skills in the following grades.  That way, your son will always have the opportunity to be with kids he can understand.