I believe it depends on the child. Some children prefers to study on their own, some want tutors. Parents' job is to encourage the child to study and give him/her the hunger for knowledge. Honestly you can't force children to learn anything. If they dont't like it, it'll go in one ear and out the other. Some people are talented in other things beside academic studies. All in all, if your child says he/she can't catch up with school work and want tutoring, by all means go get one. You can always ask if he/she want tuition, if the child says no and you thinks it's necessary that he/she has extra classes, ask why the child doesn't want it. Then maybe you can know more about your child.
Just my 2 cents... I believe in the "you live, you learn" saying. I dont't mind my child failing as long as she learnt something out of it.