it doesn't work for every kid, but it worked for mine... and I'm good all right... at bargaining, coercing, and (if needed) bribing... having Damian be off the charts for height yet only 18mo 8 days older than Jeffrey made it a necessity early on for Jeffrey to be okay with being harnessed while his brother wasn't anymore, to be in a booster past the age his brother had left them behind...
Ruthie, fortunately, is not as bad about it (now that she's older) because she's heard me preaching for so long that it's not about age ENTIRELY... it's also about size, maturity, and (when it comes to the highback/backless/no booster thing) the seatbelt fitting properly.
this past spring/summer she was asking for a backless... until she felt how the seatbelt was not as good of a fit, she had nowhere to rest her head, and she doesn't have that protected feel from the upper part of the booster around her body... so she knows why she's not ready for one yet... except in a rare occasion. Now when the vivo expires in 2013, I'm hoping she'll be ready.