Good experiences. There is a critical mass of gifted kids and a dedicated (in both senses) group of gifted teachers. They always "get it" when I ask for customization, and they are responsive and sensitive. Acceleration is simple -- pick the level your kid is ready for, and take it. My 7th grader took Honors 10th grade English and Honors Algebra and HS French, all no problem. As a 9th grader, DC will be taking AP classes.
That said, it IS, IMO, still very much homeschooling-flavored. By that I mean that the actual teaching is done by the parent or tutor at home. LSS is very upfront about this. Their teachers are definitely available for curriculum customization and student/parent questions, but the teachers don't lecture or provide presentations. Parents/tutors have to do that. So, for example, language learning has to be done by the parent/tutor; there is NO way a kid could learn a language from the book or online materials given.
So what we like is the range of courses and the customization -- if you want, say, more modern novels and fewer short stories, and if what you want is academically respectable, you'll get it! Or a long research paper added in. The teachers are excellent, and they grade rigorously, especially in the honors courses. The Honors courses have zero multi-choice work; it's all writing. So if your kid doesn't like to write, this might not be the school for you, but we love it -- DC wrote something like eight 1500-word essays in English this year, plus probably another ten "two-page" (500-800) word essays, plus 1000-2000 words of additional weekly short-response questions. The questions are nicely analytical -- not just plot-checking.
We like the credentialling value and the reality-check/feedback aspect: the teachers grade the work, give feedback, and have a sense of where your child is compared to others. DC will graduate with a transcript from an accredited school, and the curriculum is common-core aligned, etc.
The downsides (not for us but for others in different situations) would be that you need a parent/tutor capable of teaching the whole curriculum (we have, between us, degrees in a range of subjects from English to social science to math plus high-level competence in three languages and one of us is a professional writer). Gifted kids can certainly teach themselves a lot, but I don't think I'd expect any kid to complete high school with no real-time teaching.
Another downside (not for us) is that I suspect that the science curriculum needs a heavy parental/tutor presence if it's going to be engaging and rigorous. None of us, including DC, are science-oriented, so reading a textbook plus kitchen labs plus some research papers are fine for us, but I don't think that approach is going to satisfy a science kid or generate a Westinghouse candidate.
For humanities, we've found the courses (especially taking into account the acceleration options) to be great. DC was reading HUCK FINN and "Beowulf" when the kids in the local "difficult" private school were reading JOURNEY TO THE CENTER OF THE EARTH and LORD OF THE FLIES (both of which DC had read eons ago).
What to ask for/watch for: I have a sense that the non-Honors courses are more multi-choice heavy. Don't take them, or ask for customization (JMO). I would also watch out for any vendor courses. We have found that the courses created in-house by Laurel Springs are serious, well-done, and (at the Honors level) writing- and analysis-intensive. But they do offer some vendor courses (Middlebury/Power Speak languages and the occasional Apex offering), which I dislike. You have to dig and ask or else be prepared to try the courses and switch (which they are quite generous about).
