Emphasize "proven". After questing the audience take a pause for thought. While asking the question open hands up.
It is a proven fact that teens naturally go to bed later and wake up later than fully grown adults. If this is true why are teens forced to get up early drag themselves out of bed and go learn before their bodies have even woke up?
Point to yourself when you say "my". speak louder when saying your opinion.
In my opinion I believe that high school and middle schools should start at a later time to increase the amount of sleep teens are getting to improve their health.
Move your head as your are talking and look at all your audience members. Emphasize "breakfast".
One reason why schools should start later to allow teens to get more sleep is because when teens are rushed out of bed and forced onto buses they often end up skipping the most important meal of the day breakfast.