You will be a rated player in North America after you've played in your first tournament sanctioned by the National Scrabble Association. Ever after, your rating will go up or down based on your performance against other rated players. Rating calculations are performed on the results submitted by tournament officials after each tournament.

The rating formula was developed in the early 1980's by expert player Alan Frank, who developed a formula similar to that used to rate chess players. The actual calculation is relatively straightforward though a bit heavy on the math, requiring computations based on probabilities of winning derived from the normal, bell-shaped curve common to many statistical distributions.

To keep it simple, your rating will go up for each game you win, and go down for each game you lose. When you play someone near your own rating, you've (theoretically) got about a 50-50 chance of winning and both players have about the same number of rating points on the line. When you play someone far above your rating, your winning expectation is very low and your rating changes very little if you lose because you merely matched the expectation. On the other hand, if you win, your rating increase will be near the maximum possible, because you defied expectations. Of course, the converse is true for your opponent. A much higher-rated player has little to gain and much to lose, from a ratings standpoint, when playing a much lower-rated player.

Some players misunderstand what happens when unrated players are part of their playing field, usually because of the misperception that such players have a zero rating. Generally, unrated players have little untoward effect on the ratings of others, because the unrated player's rating is determined, by a trial-and-error method, after the fact. That is, they are considered as having a rating they earned for winning however many games they won. Even if they win no games, they start with a minimum rating (500 after their first tournament), and go up from there.

Experienced player ratings range from under 400 to over 2000, with the largest number rated near the middle of that range. There are a wide variety of tournament formats, and some players choose to play in those that are most advantageous to their rating goals. Other players don't care that much about their rating, but still appreciate the knowledge ratings give about the playing strength of their opponents. Most players understand that their rating will fluctuate. Players who seriously work at improving their game will see their rating generally rise, possibly into the expert range. Players who reach a rating plateau will see their rating vary about 100-150 points around an average, or approximately true, rating. The very best players may have nowhere to go but down, but those who continue to work at their game generally remain near the top, despite occasional rating disasters.

There is some controversy about ratings, for a variety of reasons. The two main reasons involve the luck factor inherent in Scrabble^®, and the observed tendency for ratings to deflate over time. Both have led to many discussions on revamping the rating calculation to more accurately reflect reality. To date, some research has been done and suggestions made, but the current formula has survived. Despite its perceived shortfalls, it has generally served its purpose and ranked players fairly accurately with respect to each other. The top players, those who win the most often and place consistently high in tournament standings, are indeed the highest rated players. Everyone else falls more or less in line below them.