One gap, and tiles that only slide
The board has numbered tiles and one empty space. You cannot pick tiles up, you can only slide them. Tap any tile that sits right next to the empty space, and it will slide into the gap. By sliding tiles around, work the numbers back into order, from 1 in the top left to the last number, with the empty space at the end. Fewer moves means a better result.
Solving it one row at a time
The whole trick is to stop trying to place every tile at once and instead lock in one row at a time from the top, then the left-hand columns on the 4 by 4 board, leaving the rest until last. Because there is only one gap, sliding a tile home usually means walking the empty space around to nudge others out of the way and back, so before each move think about where the gap needs to be, not just the tile. Begin on the 3 by 3 board, where a row-by-row plan is easy to see, then step up.
Planning several slides ahead
A sliding puzzle is a tight little test of sequencing, because the single empty space forces you to reach the goal through a fixed, fiddly set of moves rather than just picking tiles up where you want them. A child has to plan a short chain of slides ahead, foresee how moving one tile will shove its neighbors around, and hold the finished picture in mind the whole way. That is the same look-ahead thinking behind following steps in the right order, and the constraint of that one gap is exactly what makes solving it feel clever.
Frequently asked questions
How do you play the Sliding Puzzle?
The numbers are mixed up with one empty space. Tap a tile next to the empty space to slide it across. Keep sliding tiles until all the numbers are back in order from 1 to the end.
How do you solve a sliding puzzle?
Work it one row at a time from the top, then one column at a time down the side, rather than trying to place every tile at once. Because there is only one empty space, moving a tile into place often means nudging others out and back, so a steady row-by-row method beats random sliding.
Why is there an empty space in the sliding puzzle?
The single empty square is what lets the tiles move at all: you slide a neighboring tile into the gap, which opens a new gap somewhere else. With no empty space the tiles would be locked in place, so that one hole is the whole mechanism of the puzzle.