this is a somewhat common problem so don't despair. First, be firm. do not provide alternatives such as diapers to facilitate the behavior. work with his pediatrician and school to achieve self esteem and a good outcome. Don't not be afraid to say how you feel, just don't project how others may feel. At five or most likely kindergarten age, school may be a goal which may not be there if he is not continent of stool.
Usually, working with your pediatrician, you can prevent stool holding, constipation, and get him going with the program.
Go to your library and get the book "Everybody Poops" and read it to him and there are others like it for boys.
Wayne Yankus, MD, FAAP
expert panelist: pediatrics