What makes the most sense for me for Rose is that she is indeed enrolled in a school in the town 40 minutes away, but Roxy is simply drunk too often to actually drive Rose for 40 minutes twice every day so she ends up missing a lot of class (which prevents her from forming irl connections, a "homestuckness" which all the guardians are responsible for in their own ways, ways which don't even require the kids to not be enrolled in school except for Jade obvs). It's all a pretty elegant extrapolation from the premises given.