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retrogress-verb  /ˌrɛtrəˈgrɛs, ˈrɛtrəˌgrɛs/ Pronunciation Key - Show Spelled Pronunciation[re-truh-gres, re-truh-gres]
1. to go backward into an earlier and usually worse condition: to retrogress to infantilism.
2. to move backward.

http://dictionary.reference.com/browse/retrogress

Just when she thought her kindergartener was making progress in his behavior, he retrogressed to screaming tantrums and throwing things.