I just moved by 46"/46lb almost 6 year old to this a couple weeks ago. He loves it - he's at level 3 for the headrest. He fell asleep on the way home from camp and didn't slouch out of it at all, even though I never mentioned looking up to him (wasn't expecting him to fall asleep!) He can buckle and unbuckle himself in both the second and third rows of our mazda5 (and it works well with the wonky seatbelts back there). I have him in the second row though, partially because he kept unbuckling the frontier next to him.