No, it isn't necessary. It's probably fair to say that most children who take stimulant medication take it only during the school week, and not on weekends, holidays, vacations. The important question to address in this regard is the child's need for the medication, and the degree to which the symptoms interfere with functioning at home and in the out-of-school settings.
My son has been on Aderall, Ritalin, Concerta and now Focalin and without it on the week-end he can't function. I think you should consider if he is involved in activites on the week-end and if so, would it help him focus better. Everyone is different and if you feel or your child feels he does better then give it a try..make sure you inform your doctor.