Mongo command

db.courses.aggregate([
  {
    $match: {
        students: "52868c8f38f0777b4e000007"
    }
  },
  {
    $unwind: "$assignments"
  }, 
  {
    $group: {
        _id: "$students",
        assignments: {
            $addToSet: "$assignments"
        }
    }
  }
]);

Result

{
	"result" : [
		{
			"_id" : [
				"52868c8f38f0777b4e000007"
			],
			"assignments" : [
				{
					"_id" : ObjectId("529fb8fa27a7a0af6700000a"),
					"title" : "Final Basket",
					"posted" : 1386199290228,
					"due" : 1388964600000,
					"completed" : [ ],
					"description" : "The worst basket you've ever made"
				},
				{
					"_id" : ObjectId("529fed5e7e3366530d00000c"),
					"title" : "No attachments",
					"posted" : 1386212702334,
					"due" : 1386212663970,
					"completed" : [ ],
					"attachments" : [ ],
					"description" : "My desc, no attachments"
				},
				{
					"_id" : ObjectId("529fb339cc75ece5a9000009"),
					"title" : "Should not see",
					"posted" : 1386197817901,
					"due" : 1386103628000,
					"completed" : [ ],
					"description" : "Due in past"
				},
				{
					"_id" : ObjectId("529fb8e227a7a0af67000009"),
					"title" : "Final Basket",
					"posted" : 1386199266481,
					"due" : 138896460000,
					"completed" : [ ],
					"description" : "The worst basket you've ever made"
				},
				{
					"_id" : ObjectId("529faec5a64e5c6717000009"),
					"title" : "Basket Case",
					"posted" : 1386196677751,
					"due" : 1386910800000,
					"attachments" : [
						{
							"path" : "759a0f4dfa55bb90d8304879a57ae6ec/",
							"basename" : "debian-7.2.0-i386-DVD-1.iso.torrent",
							"uploadPath" : "uploads",
							"_id" : ObjectId("529faec5a64e5c671700000c")
						},
						{
							"path" : "7068add94e96bcfae46fd738581f3d45/",
							"basename" : "debian-7.2.0-i386-DVD-3.iso.torrent",
							"uploadPath" : "uploads",
							"_id" : ObjectId("529faec5a64e5c671700000b")
						},
						{
							"path" : "e303be466daa64bea3a96508aa4679ef/",
							"basename" : "debian-7.2.0-i386-DVD-2.iso.torrent",
							"uploadPath" : "uploads",
							"_id" : ObjectId("529faec5a64e5c671700000a")
						}
					],
					"description" : "Make a basket."
				},
				{
					"_id" : ObjectId("529fad79c9866e0c63000008"),
					"title" : "Test 3",
					"posted" : 1386196345140,
					"due" : 1386196316956,
					"description" : "TEEESSTTTTING 3"
				},
				{
					"_id" : ObjectId("528a8fb6526c429a2e00000b"),
					"title" : "Nick's assignment",
					"posted" : 1384812470768,
					"due" : 1384812464060,
					"description" : "asdfasdfasdf"
				},
				{
					"_id" : ObjectId("529d0a17c015167c71000007"),
					"title" : "Chapter 8",
					"posted" : 1386023447107,
					"due" : 1386046800000,
					"description" : "New assignment for chapter 8"
				},
				{
					"_id" : ObjectId("528e20c37973fe8b5e000007"),
					"title" : "Zac",
					"posted" : 1385046211646,
					"due" : 1385046205813,
					"description" : "asdfaadsa"
				},
				{
					"_id" : ObjectId("529fa946d4465391f300000a"),
					"title" : "Bee Skep Basket Project",
					"posted" : 1386195270793,
					"due" : 1387658828000,
					"description" : "Baskets submitted that have been purchased from Michaels will not be accepted"
				},
				{
					"_id" : ObjectId("528a8f7d526c429a2e00000a"),
					"title" : "Mike's assignment",
					"posted" : 1384812413179,
					"due" : 1385355600000,
					"description" : "asdfasdfadsfs"
				}
			]
		}
	],
	"ok" : 1
}


// WHERE "_id" is the student's _id and "assignments" is the student's assignments