I only know from my son and other people who have tried, but restraining causes more problems. You are talking about touch, possible phobia of not being able to move, etc... That could be the cause of not liking the booster seats. I can't say I agree with the "outgrowing" of SPD. My friend told me that too, that her son "outgrew' it. I don't think so. I think you learn to "adapt". Your sensory system is not wired correctly it just doesn't rewire itself. My friend's son has more problems as a teenager, he has tried to commit suicide, she has had to have him in therapy in a hosp., he was very odd as he got holder, severe temper , he never had early intervention, both him and his brother were very spoiled, not that has anything to do with anything, but there wasn't any structure. If you were able to outgrow it I think there wouldn't be adults on here with the issues. Just my own personal opinion, I think it is more of learning how to adapt to your situations, and that comes from therapy, support, etc. Learning how to use those coping skills that were taught to you through out life. I would not want you to sit on this belief that it could possibly be outgrown, that is not fair to you. It is through a lot of patience, consistency, a few bottles of wine, but it will pay off in the end. We are not given anything we cannot handle. I was given this child because I can handle this, because I was meant to help other children with similar issues, it is very overwhelming and takes a selfless person to do it. I know you can and in return you will be rewarded with the most awesome person ever! Once you get the behavioral patterns in play, the "sensory diet' down it will be easier!!!! We are all here for you !!!!!!