There are two chains of Crumbling tiles that are isolated from the rest. And the number of crumbling tiles in those two sets adds to, 25. So to get this achievement, you'll have to dislodge the two chains of crumbling tiles that aren't connected to the rest. This achievement may be hard for beginners because the second crumbling tile chain is pretty tiny and easy to miss. Also, you may touch one of the crumbling tiles that are connected to the rest. Oddly, the main chain of crumbling tiles can be dislodged first, and still grant the achievement most likely because the game tracks if you break the two smaller chains of tiles consecutively. As usual, the Runner is recommended because she is easier to control than the Skater.
This may sound ridiculous, but the Child is good too because he can jump off the required crumbling tiles but has less risk of dislodging additional tiles.
The Student is fine for this, given that she can adjust her jump length, she will have not much a problem of avoiding excessive Crumbling tiles.