My son was there for 10-12 (he graduated 5 years ago).
The kids are placed by ability, and most classes are extremely rigorous, although I supposed one could always asked to be placed in grade-level class if the student needed extra bandwidth for outside activities such as sports or the arts (some international athletes and artists did just that). It did feel like a school while he was there. The kids met up frequently via Skype (i think the platform has changed since he was there) and Fridays are devoted to school clubs. There are several all-school meetups each year (two on Stanford campus and one at MIT) and if you live near other OHS students and there is an active parent group, there are frequently multiple activties a month that the students can go to (organized by parents and/or students).
The school is a 7-12 school, even though it is called a High School. What grade level is your student looking at?