My DS7 did early entrance into kindergarten. He is now in second grade and accelerated an additional year in language arts, joining the advanced 3rd grade reading class. Its has been working really well this year. Sometimes a one-year acceleration might not be enough though. This is the case in math for us. They offered to accelerate him but him working at almost highschool math it just wouldn't have made a difference to accelerate a year or two. Make sure the acceleration they are offering will be enough. They make it sound good when they were open to subject acceleration, but it still might not be enough. My son is working independently in math with EPGY.
At this point scheduling is not a problem since all lower school language arts classes are at the same time. The principal has talk to me about the transition from lower school to middle school though. He might have to do the fifth grade regular class when he's in the fourth and then join his class for the fifth grade advanced class when he is in 5th. We will deal with this when we get to it. But it sounded like the scheduling will be nearly impossible for him to still be in 5th grade and doing the middle school 6th grade reading class.
