Calvert we have some experience with. My DD was six and seven then, though-- so a bit older than your little one.
One thing that I'd offer as an observation about this (or any other PACKAGED curriculum) for a HG+ child...
while the curriculum may have a very nice focus on literacy, this is simply NOT well-aligned to the needs of a young HG+ student. The literature/reading is simply far too little, and with a child who is already reading and has good numeracy, it's torturous. Why? Because of all that writing. There's no payout for putting up with all. of. that. writing.
The math is very shallow, IMO.
It's not a bad curriculum, by any means. The problem is that it is bundled and hard to subject accelerate within, meaning that a child who is ready to read and do math at 2nd grade, but has age-appropriate kindergarten writing skills (or, as is likely in your 3yo, more like preK skills)... winds up feeling a lot like Goldilocks. NOTHING about it fits, but a lot of it "almost" does-- on both sides. The writing is too hard (out of level) and the rest is still too easy and wayyyyyyy... toooo... slowwwwww.
We found that this was true with every "bundled" prepackaged/all-inclusive curriculum that we tried. The reason is that there ISN'T a homeschool curriculum intended for the particularly common patterns of asynchrony found in HG+ learners at young ages.
My personal recommendations for this age are Montessori at home (there are books that detail how to replicate some of the Montessori methods as a homeschooler) and Charlotte Mason (without the rigid elements and with more math/writing as seems appropriate for your child and family).
That means going a bit piecemeal and eclectic, it's true-- but it is about the only way to get an appropriate fit at these earlier grades. HG+ preschoolers and primary students are often way out of synch with the abilities of age-mates.
