When playing Road to Glory Mode you will have the chance to play in a High School Championship game at the end of the season. The play-offs will consist of 3 games before you reach the championship game. You can simulate through the season to get up to the championship game, but you can NOT simulate the championship game in order to get this achievement. You must play and win game for it to unlock.
Also note that you MUST have the sliders set to DEFAULT. If you have custom sliders on while playing the game, the achievement will not unlock.