Make sure you count how many tiles you dislodged accurately. If you dislodge 8 or 6, you will have to keep playing until you reach this level again, which might take a while.
One strategy is to dislodge 5 of them ASAP, then dislodge 1 crumbling tile in the middle, then dislodge 1 crumbling tile at the end. This strategy gives more room for mistakes.
Even if you don't keep track of how many you have dislodged, once the progress bar does a sudden jump, you know you have dislodged 7 tiles. Dislodge no more.
The Runner is good since she has great control when running. This can help her to avoid the extra Crumbling tiles while dislodging the others accurately. The Student is pretty good as well since her speed is quite low, she can maneuver and avoid the excessive Crumbling tiles easily, and her special ability can let her avoid many Crumbling tiles after you dislodged seven of them (required), and this saves you a lot of trouble. The Pastafarian can break all seven tiles right away, and then use the light bridge to effortlessly avoid the remaining crumbling tiles.
One last tip: Never use the Duplicator on this level (even though the achievement is called The Duplicator's Lucky Number). His duplicates can dislodge tiles as well, making it extremely hard to avoid the excessive Crumbling tiles, and makes it hard to count for the accurate number as well. For this reason, the name of the achievement is very misleading. Furthermore, the Child also makes this challenge difficult, as the process of jumping off the tiles and then floating down again is time consuming, and often does not leave enough time to dislodge seven tiles.