I would start with the back office first, get them to learn how you do things from the office. That way they have some knowledge of how the info you gleam from "in the field" incoroprates into the whole investigation.
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What might me quite cool for them is perhaps on the first morning take them out and about and show them the work you do. This will get them interested and wanting to get out and do it. Then have them on the backend stuff for the first week as you say, then the next take them out all week. That way they won't get bored in their first week as they know the juicy stuff is yet to come!