Most parents who are unhappy with their children's education write a letter to the principal or, as a measure of last resort, take their child to another school.

Not so for tech entrepreneur Elon Musk, the man building rocket ships and electric cars, funding artificial intelligence research and working towards a vision to colonise Mars.

Tech entrepreneur and SpeceX chief executive Elon Musk. Credit:AP

Dissatisfied with his son's schools, Musk has bought a mansion in California and created an experimental primary school with no grade structure for just 20 students, including his sons.

Ad Astra, Latin for "to the stars", has three teachers, no website and no obvious application process.