The OP overview did mention some studies. (The OP overview is a really good model for a popularly-accessible summary of research on a complex topic! it lists so

The OP overview did mention some studies. (The OP overview is a really good model for a popularly-accessible summary of research on a complex topic! it lists so much stuff!) I'm not saying this necessarily should eliminate all worry you have about attachment (personally sleep-training seems like a bad idea to me too; I'm not a parent however), but as far as what research is available, from the OP: > Of the few studies that have looked at the short- to longer-term outcomes of sleep training, none have found an effect on a baby's attachment or mental health. Hiscock's study, for example, the largest and longest longitudinal study done on sleep training, found sleep-trained children were no more likely to be insecurely attached to their caregiver at six years of age than their peers. (Experts like Hiscock say they aren't aware of any studies that look at potential long-term effects of cold-turkey cry-it-out, just at modified extinction. They also examined healthy babies at least six months old. So these findings aren't necessarily applicable to infants trained at younger ages, or in other ways.) > Like other longitudinal studies, Hiscock's lost touch with a number of families when it was time for the final follow-up: 101 of the original 326. That means it is theoretically possible that the sleep training did affect some children in either a negative or positive way long-term, but that their experiences weren't captured. It's more likely, though, that any effects of a single intervention simply "washed out" after six years, says Hiscock. https://www.researchgate.net/publication/230830539_Five-Year_Follow-up_of_Harms_and_Benefits_of_Behavioral_Infant_Sleep_Intervention_Randomized_Trial https://www.researchgate.net/publication/230830539_Five-Year...