I'm just agreeing with Lourdes' wise advice here! The independent history box has many skills attached to it, and you are right, it's important to do.

The extensions are wonderful too, but if you are needing to choose between the two, I'd have ds read the extensions independently on his own time, and not do the follow-up extension assignments. Or, if the reading of the extensions proves too much, I'd save them for later. My ds never does the extensions while we are doing the core program as he's on the young side of the guides, but he always reads them at some point down the road - they are excellent books. HTH!
In Christ,
Julie