I think it depends on age, my sons got lessons in 6 week segments from age 10 to 13. Once a week with instructor then reps with dad, from 13,15 they joined a travel team that had coaches who reinforced and or tweaked things a little bit, at 15 and continuing forward they do lesson in the offseason every other week. As they grow and mature the lessons are much more approach based and less mechanical. As kids mature the needs change from the instructor.
so basically it kind depends where your son is in the time line of his baseball swing.