"Textbooks are not meant to instruct teachers what to do but to inspire them to bring to life well-researched lessons."

     - Yeap Ban Har, Make it Stick

I believe the most powerful math learning takes place in small, incremental steps with consistent, meaningful reviews. Therefore, I recommend that the first 45-50% of each math class be devoted to fluency and problem solving that covers previously learned topics. I think that the lesson itself can last any amount of the remaining class period so long as teachers are delivering frequent informal assessments and students are receiving meaningful practice.