Scales are ordered sequences of pitches. They can be mapped to the fretboard as a specified number of notes per string (each scale type then has a certain shape for each mode), but there are many other ways to map scales to the 'ukulele fretboard:
1) play the scale on a single string;
2) play two or three notes of the scale per string;
3) incorporate the reentrant string into the scale;
4) play 2 octaves of the same scale (this will generally offer many options for choosing when to change positions)
....and so on.....
1) emphasizes fretboard knowledge, 2) improves position playing, 3) provides more campanella and fingerpicking options, and 4) is good for practicing position changes. There are many, many other approaches to scales, but this is a starting place.