Level IV is a level of "service" that is provided to kids who need advanced academics. Level VI is the highest level. It's gotten really confusing:
there are Level IV Center AAP programs (Franklin Sherman kids who qualify for Level IV services are able to go to Haycock, their designated center, for classrooms that are comprised only of other Level IV kids).
there are "Local" Level IV programs (for example Chesterbrook has a local program, which means Level IV kids can still choose to go to haycock, their Center school, but could also stay and receive Level IV services in the home school. It's done differently at different schools, but at Chesterbrook many of the Level IV kids stay. They are mixed in with the rest of the grade, but have some separate classes for reading, math, SS, etc, and in fact many Level III kids also attend them. (Level III are kids who did not qualify for a Center Program, but are considered very bright and in need of additional/supplemental curriculum.)
NOW, they are now offering a Level IV "curriculum" to a number of McLean Elementary Schools. Which seriously adds to the confusion. But this is not a Center program, OR a local level IV program. It is a different curriculum for grades 3-6, and I think it means that they are trying to teach differently and/or add in more supplementary ways to teach (maybe more hands on, maybe more accelerated pace in some subjects, maybe more school plays about academic subjects).
FCPS was very unclear when they announced the level IV curriculum being taught in all the mclean schools. It is hard to disern what the changes in curriculum will be. but it may mean that more Level IV eligible kids will stay in their home schools in 3rd grade, even in schools that don't offer a formal "Local" Level IV program.
BTW, many Franklin Sherman parents have tried over the years to get a "local"Level IV program in their school, similar to Chesterbrook's. it may be that this curriculum change is a response to that desire. it will be interesting to see what the difference will ultimately be between the local Level IV programs and the Level IV curriculum for all kids.
hope that helps.