Which marketing innovation led to the widespread adoption of the 'Singapore Math' textbooks and methodology in schools outside of Singapore during the early 2000s?

The mathematics textbook market has seen significant innovations in marketing strategies over the decades. Publishers have employed various techniques to differentiate their products in this competitive academic space. One particular marketing innovation revolutionized how math textbooks were perceived and adopted by educational institutions. Test your knowledge of this significant product marketing milestone in the mathematics education industry.

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Bar modeling visualization technique that made abstract math concepts more accessible
Celebrity mathematician endorsements featuring Fields Medal winners
Augmented reality components that projected 3D geometric shapes
Subscription-based pricing model with monthly problem set updates