The Same Word, Three Scores
34 percent of words score the same in both games. The rest do not.
The Number That Surprises People
Of the 73,581 words between four and seven letters, only 24,880 score the same in Scrabble and Words With Friends. That is 34 percent. For the other two thirds, a Scrabble instinct gives you the wrong answer about which play is bigger.
Where The Gap Is Widest
Words With Friends values J at 10 against Scrabble's 8, and U at 2 against 1. Stack those and the gap opens up fast: JUJUTSU, JUJUBES, JUJUBE all score up to 7 points more in Words With Friends than in Scrabble. The reverse case is milder, because no letter is worth dramatically more in Scrabble than in WWF.
The Practical Version
If you play both games, do not carry a scoring instinct between them. Check the actual number. The Words With Friends Cheat and the Scrabble Word Finder rank the same rack differently for exactly this reason, and Check Dictionary will give you both numbers for a single word.
More like this in the guides index, or put your own letters into the Word Unscrambler.