The reason I sacrifice my class time and push them to tournaments are:
First, tournaments are where they apply and test the knowledge they learn. This is the only way they can master the skills solidly.
Second, tournament environment is much more serious than class environment. You don't know most of your opponents, and everyone wants to beat you. When you are serious, you think more and think better.
Third, winning a tournament is a big confidence booster. Your child will be much more interested in improving him/herself.
Fourth, playing in a tournament is also a small goal. If you perform well in small tournaments, you may go to state tournaments or nationals. All these goals are motivating your child to work hard. Without goals, where can you reach?
My best students are in Step 4 class. All of them are playing in the tournaments. I track all my students' tournament progress. If I see some previous students stop playing tournaments, I know I would lose track of him/her pretty soon. Very likely, s/he will stop playing chess completely.