Hi Christopher,

The more games they can play the better! They need to spend as much time with the ball in their hands as possible. Play small sided touch rugby games (5v5, 6v6, etc). Whilst it's important for the boys to be handling the ball, you can also organise the games so that the defending side has to work on realignment. Eg. When a touch is made, the person that made the touch must go to the floor, ball carrier puts the ball through legs but the attack can't play for 3 seconds. This gives the defence time to get into position, rather than focus on the ball/tackle.

Once they're realigning better, you can decrease the time available, or make the defenders do an activity (press up or run to the side line) before getting into position. Running to the touchline can make it slightly more game realistic as players reach the tackle/ruck at different times, so need to work out which holes need fiilling first.

By doing this, the defenders know they can't compete for the ball, so they really concentrate on their positioning. This can then be taken into more 

By playing these games, there's lots of ball handling, but the players can also focus on defensive alignment, without even realizing!

You can also run practices where the boys/girls are in a defensive line, you throw a ball in front of them. The person that's in line with the ball dives on it, the nearest player stands over the player and the remaining players realign again. You can continue this and maybe add extra activities, as mentioned earlier, so that the players start to get to the tackle area at different times.

Hope this helps!