Intrinsic motivation is a big part of Montessori education but this link is not about my Montessori cult worshipping so feel safe to click on it. This is a pilot program looking at an independent learning high school in the US. One of the best bits starts around the 8 minute mark where the students talk about how they problem-solved making maths interesting for themselves. There are too many terrific quotes in here to pick just one. Just so much going right here.
(Thanks to Buffalo Mama for the link).