I make it a condition for my kids when moving into a booster in a position without lower anchors/moving to a seat without lower anchors. "If you can't buckle it every time, you're not allowed to have the seat, because I can't have it flying and hitting Abba or me or your sister in the head if we make a sudden stop." The eldest had a hard time remembering at first so I did select a booster with LATCH for her at first (at 7) but the second had no trouble when she moved to a booster at 6 years 9 months (she's a rule-follower in the car. She also tells her Grandma that it's not safe to turn around in the car because you are out of position and it's dangerous. LOL) I finally moved the 10 year old to a backless and she has not forgotten once either this time. (I do occasionally, if we are in a hurry and no one will be in the car again until they are back in their seats, such as all of us getting out at church or to go to a family dinner, give them one-time permission to skip buckling because no one will be in the car to be hurt by flying boosters. But other than that, they do it, and mostly without grumbling. Once in a while when it's late the ten year old asks if she has to but when I say "Yes, because Abba will be driving in the morning without you" she pouts, but takes the five seconds to do the belt up.)