Some things are nearly impossible to learn later if a certain foundation has not been prepared early-on. For example, adults speak foreign languages with an accent unless they have heard and spoken some of the sounds before about the age of 10. During a 24 hour day, there are certain times when most people learn more easily. Then there is a dip in performance for 30-60 minutes, followed by a second, lower, peak, that gradually tapers off. This is caused by the natural rhythms of chemicals in the body.
Adolescents take longer to reach that first peak in the morning.
Their afternoon dip occurs a little later in the afternoon and their second peak is more sustained and stronger. Dr. Sousa suggested that extremely early academic schedules discouraged teenagers due to this natural rhythm that many teens exhibit. He suggested that athletic activities before the academic classes helped students to reach a higher level of alertness by the time core classes began. If you are in a position to teach after lunch, focus on shorter activities and hold students accountable for the new learning. For example, instead of assigning a chapter of silent reading, read one page and have students discuss how they would have handled the situation differently than the main character.