Have a 4 month welsh springer spaniel who is lovely except that when I go out he barks and howls - so the neighbour has told me!. I do not leave him very often but inevitably with 2 children I do have to leave him in by himself sometimes. In the house he has not been happy about being left downstairs when I go upstairs (babygate in use!), but is getting much better and I've seen real progress here. I have a crate but have not really shut him in it very often, but today for instance he went in there and I shut the door and left the room and after a few whines for about 5 mins he settled down and slept for just over an hour without me going back in the room.
So I want to train him to be in the crate when we're out and at night. Any tips from anyone as to how to go about this?  I have been advised that this should be a good way to stop him barking but I suspect that as soon as I shut the door, the barking will start! I am assuming I will need to leave but then stand outside and see what happens. If he barks I thought I should leave him at first to see if he settles and if not return to do what? Reassure or reprimand? If quiet then obvious loads and loads and loads of lovely praise!! Once he learns to be quiet I could then extend the time I stand outside and build it up that way. Has anyone out there done something similar and how long did it take? Also would a DAP diffuser make any difference? I've read conflicting things about these so not sure whether worth buying. Any help/advice much appreciated. Thanks!

It sounds as if he's already most of the way there - the crate should always be a place where positive things happen - maybe feed him in there?  When he does need to go in there, make it rewarding for him by providing something to safely chew.  NEVER release him or go to him when he barks.  Many dogs find a crate even more welcoming if it is covered in a blanket - but make sure he can't pull the blanket through and chew it.  If you have to make frequent trips out and use the crate, then it's going to be hard to train, as there will be periods when you aren't there to react (or not) in any way to his behaviour.  But it sounds as if he's already a long way towards accepting the idea without you actually having to do too much.

BTW - IMHO neighbours don't always tell the truth about how much a dog barks, it may be worth setting up a tape recorder or video camera so you can see yourself how your dog reacts while you aren't there - you may be pleasantly surprised :)

Seperation anxiety is very common in this and other Spaniel breeds and you are doing the right things by getting him to accept short peroids of alone time.