I let them cry it out. When they are transitionning I do the 5-10-15 method but when they are doing well during the day and only cry at nap time... I let them cry. I make sure to tell them they are OK and that ''I will see you when naptime is over' In a calm voice. I can always see them whitout them seeing me. So far it has worked well for me but I did have this little girl part-time start in January and she JUST started to nap whitout crying/screaming. Almost over 2 months of cry/scream EVERY NAP TIME but now she sleep over 2 hours almost everyday. Get yourself some headphones