Wikipedia
Micro-schooling refers to any school where students meet two days or less each week to take classes, where class size is typically smaller than most schools (15 students or less in a classroom), and classes are taught using a flipped classroom approach, a form of blended learning. Classes tend to be more impactful due to meeting fewer times in the week and these classes are typically hands-on and activity based. Together this approach is viewed as a replacement for the 5-day school week paradigm that is standard world-wide.
Micro-schooling is seen as being in between homeschooling and private schooling and is designed to offer a full-year of education at under $10,000. It's growing popularity stems from a general dissatisfaction of how schools (public and private) often structure their content. Homeschool families are drawn to the idea because of how micro-schooling establishes a core set of learning experiences similar to what might be found in normal schools that parents can then expand on and individualize for their children. Private and public school parents see micro-schooling as an affordable option that provides their children with a more worldly education that some might consider as Constructivism (learning theory) in approach.