This is another option for middle school. Start with the 6th grade level and go through all the levels.
For Middle School math, you may want to check out Master Math. Start with the 6th grade level and then complete levels 7th and 8th for a full curriculum. There are 110 lessons.
For High School, we have had relatively good success using Khan Academy. It can be used as full courses or as homework help and tutoring.