How can I persuade my mum to let me go to an after prom party?

My dad s letting me go because parties are appropriate for my age, I m nearly 16, and it s a good experience on what life would be like as a young adult I m soon to be. But my mum says no, just because she wants me a keep being her little boy, she can't accept the fact that I'm growing up, and I might even have one glass of beer. Thanks (: