How do I reorder Structure entries on the front-end?
The place to do that sort of thing is StructuresService.

If we’re just talking about reordering a flat list of entries (no hierarchy), the only methods you need to worry about are moveAfter() (if an entry is being dragged after another one) and prependToRoot() (if an entry is being dragged to the first position in the structure).

$entry = craft()-&gt;entries-&gt;getEntryById(1);
$prevEntry = craft()-&gt;entries-&gt;getEntryById(2);
$structureId = $entry-&gt;getSection()-&gt;structureId;

craft()-&gt;structures-&gt;moveAfter($structureId, $entry, $prevEntry);