Build through the pitch instead of over it. Get the defenders wide enough to give the keeper an angle, find a midfielder between the lines, receive on the half-turn so the next pass is forward, and only then attack the last third.
Play 5v5 plus keepers on a 50x35m pitch marked into three equal zones. Normal football with one condition: a goal only counts if the ball was passed to a team-mate in the middle third on the way up. Players are not locked into zones and may move anywhere, since locking them in removes the decisions the game is meant to create. If a team goes long and scores, it does not count and play restarts with the keeper. Play six-minute games, rotate the keeper, and take the condition off for the final game to see whether the habit survives without it.
The step up to a bigger pitch creates a habit almost overnight. Suddenly there is space over the top, a goalkeeper can reach halfway, and hitting it long occasionally works. It works often enough to be reinforcing and rarely enough to lose most matches, which is the worst possible combination for a young team.
Telling players not to go long does not fix it, because in the moment the long ball is genuinely the easiest available option and easiest usually wins. Removing it from the game does fix it. If a goal only counts when the ball has gone through a team-mate in the middle third, the shortcut stops being a shortcut.
What then has to be solved is the actual problem of building. Somebody must occupy the middle third, and that somebody has to be findable, which means the defenders in front of them have to be wide enough to create a passing angle in the first place.
Receiving there is the skill the condition really trains. A midfielder who takes the ball square, facing his own goal, has turned a successful build-up into a backward pass, and the team starts again. Receiving on the half-turn is what makes the whole sequence worth having.
Scanning is inseparable from that. The picture in the middle third changes completely while the ball is travelling, so a player who looks after it arrives is working from information that is already out of date.
One thing worth guarding against: teams that build patiently often stay patient once they are through, and the moment the build-up created gets wasted. Being slow in the final third is not the same virtue as being calm in the first.
Take the condition off for the last game. If the shape holds without the rule, the rule has done its job and can go away.
Save it to your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block. Or start from a blank pitch and build your own.