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n my experience most conversations at the park or museum are fluff and the odds of alienating someone that I might have other things in common with aren't worth the incredibly slim chance that they are also dealing with a gifted kid. To 98% of the population the statement of "she's beyond the curriculum..." will come off as some sort of super-tiger mom bragging and they will run away.

This. If you're looking for other parents with simialr kids, try chess, Lego, art, HSing groups, drama, even advanced athletics if your kid is inclined. There are a lot of possibilities. I don't think dropping this stuff into random conversation is likely to pan out well. Where I live, HSing is not uncommon, so a simple "We plan to homeschool" would be fine, perhaps followed up with "We think it will work best for us/we're excited to start/there are lots of opportunities" etc.