Myers examines several significant themes throughout his novel Slam, including friendship, teamwork, education, sports, and making the right choices in life. Greg "Slam" Harris is a talented teenager who lives in Harlem and goes to a private school to play basketball. Although Slam is successful on the court, he struggles in the classroom and his friends are getting involved in street life. In my opinion, Myer's main theme of the novel is how to transfer success in one area of life to another. Slam is continually focusing on his performance in basketball, rather than on his grades and relationships. His assistant coach and mother encourage Slam to take his grades seriously in order to possibly earn an athletic scholarship, but Slam believes that as long as he is doing well on the court he will be successful in life. As the novel progresses, Slam begins to realize that he needs to take life off of the court as seriously as he does when he is playing basketball. Through Slam's experiences, Myers examines how difficult and important it is for a teenager to maintain focus in sports, the classroom, and at home.

Your question isn't really fair because of the large number of themes in this coming-of-age story:  basketball, drugs, friendship, family, education, attitude, etc.  However, if I had to choose a MAIN theme, I would say, by FAR, the main theme is as follows:  TEAMWORK.

If you look at all the minor themes of this bildungsroman, you will see teamwork is involved in ALL of them.  One cannot play a team sport like basketball without teamwork.  One cannot be involved in a business (even an illegitimate business like drug dealing) without teamwork. One cannot be in a healthy friendship or a healthy family without teamwork.  (I had to laugh at that last one because I did have to insert the word "healthy.")  One cannot receive an education from teachers/mentors/professors without teamwork.  And, finally, you cannot achieve ANY teamwork without the proper attitude of respect for all.

Of course, all of this teamwork has to do with the main character of Greg:  a fantastic, young, teen basketball star who wants to eventually make it into the NBA.  The conflict of talent vs. reality is real here.  Hard work is paramount especially within the setting of urban experience.  All of this involves teamwork on the part of Greg, his friends, and his family.  Greg has to spend a lot of time balancing his "want" of attitude with his "need" for teamwork and, in that, success.  You can see this struggle in the quote below:

I'm six four, and I got the moves, the eye and the heart. You can take my game to the bank and wait around for the interest.

In the end, of course, Greg learns that "moves" and height and even talent are not enough for the success and happiness that he years for.  THAT kind of happiness only results from teamwork in an atmosphere of respect.

The novel “Slam” by Walter Dean Myers has several themes.  The story is about the life, challenges, and growth of Greg Harris.  Greg is the narrator and he is name Slam on the basketball court.  Greg is 17 and has a great deal to learn.  One of the things he must learn is that in order for him to be a success he must believe in himself.  He must realize that education is important even if you are going to the NBA.  Greg also learns the damaging effects of drugs through the experience of his friends.   But mostly Greg learns that no one can succeed alone.  Without the help and support from family and friends you can’t really be a winner.  There is no “I” in the word “team.”  Teamwork means that if you depend on each other you will all be winners.

What is the theme of the book Slam! by Walter Dean Myers?

One of the main themes of the story is the importance of teamwork. Although basketball is a team game, Slam is a bit of a lone wolf, playing for himself more than for others. It's notable that the coach starts to think of Slam as a bit of a showboat, someone who's not prepared to give his all for the team.

With all the other problems going on in Slam's life, he somehow needs to reconcile his heightened sense of individuality, both as a young man and as an athlete, with the needs of the basketball team. At first, it's pretty hard for Slam to do this. His ego holds him back from developing good relationships with his teammates, and they start getting into fights. It's only when Slam's team, Latimer, is losing to his old school, Carver, in the state championship game that he finally realizes the value of teamwork. Somehow Slam's able to put aside his ego and at long last start playing for the team, with the result that Latimer defeats Carver.

What is the theme of the book Slam! by Walter Dean Myers?

In many ways the theme is individual vs. society and the individual figuring out their place in society.  Greg is a star basketball player trying to figure out how to balance basketball, school work, and a relationship with his girlfriend.  The story revolves around him trying to figure out which one should be a priority and deciding whether or not to switch schools knowing he likely wouldn't fit in in the new school.  Of course the entire time he is also dealing with crime and other dangers in his neighborhood.