Possible Clues:

• Prince happiest flying in training period
• Period learning a trade
• Period of learning in a skilled trade
• Preppiest chain devised training scheme
• In dentures, say? They are required for one to be served
• Period for learning a skilled trade
• Paper composed by conservationists is evident around church before joint training period
• On-the-job training in oddly nice pit, perhaps
• One bound to get a packet for these articles
• Period of learning trade