MY DS is newly 10, 55" tall and still has a backless booster in my car. He does not 5 step in my Ford Edge. That said, when I send him with other families for hockey I do not send a booster, none of the other kids who are the same size still sit in a booster, in fact, my friend had her tiny tiny 6 year old who is the size of a 4 year old without any booster, I unfortunately made a comment as she had the seatbelt behind her back, I said "oh let me grab her booster from the back" as I have seen her in a booster before. The mom who is a good friend was like, oh we didn't bring it (this was a 3 hour trip). She was shocked I made DS still sit in a booster. For rides with others I"m ok, but in my car he's fine and hasn't really said too much as he knows he can see better and the belt fits better. To the OP, it's a battle that you need to decide what your comfort level is.