A whitelist is a list of accepted items or persons in a set. This list is inclusionary, confirming that the item being analyzed is acceptable. It is the opposite of a blacklist which confirms that items are not acceptable.
For the last ten years or so of providing web access in schools in the US, school districts have relied on a blacklist, a list of identified inappropriate sites to which computers within a district were denied access. Districts commonly contracted with software vendors who constantly updated that list with inappropriate sites. Staff members in that district were asked to report inappropriate sites that they or their kids happened upon so that they could be added to the database.
An example of how a whitelist changes everything:
Say a district whitelists blogger.com (very common practice). All blogs that end in blogspot.com are then blocked from within the district, effectively blocking the .06% of inappropriate blogs from blogger (I made up this stat - just bear with me). This effectively shuts off access to 99.94% of the appropriate blogs on blogger. If anyone wants access to a blog on blogger they must request an "unblock", along with rationale for the unblock. One unblocked site still leaves 99.94% (the appropriate ones) blocked.
The onus is now on the teacher. There is no wide open door anymore. If you want to see what's out there, you have to go looking on your own time, from home, jump through hoops, and cross your fingers. Teachable moments? Forget it.
There are hundreds of companies out there with blacklists that school districts could plug into their filtering software. Why is blacklisting not used anymore? It costs more. It's more work. It's not perfect. Why are districts whitelisting? It's cheap. It's relatively easy. It's safe. No kids will ever see anything inappropriate.
Heck, kids won't see anything. This approach is so obviously unethical and plain out wrong, that I cannot believe nobody is saying anything about it. Maybe nobody realizes it is happening. I've been using the web as a part of my daily classroom instruction - with third graders - for the past twelve years, and I can say this is by far the most repressive and restrictive access to knowledge that I have ever seen. I guess what sticks in my craw the most is that those in charge of school Internet filters are giving teachers absolutely zero credit - or responsibility - for being able to watch, teach, and look out for the safety of their children on the Internet.
Worrying about DOPA at this point is ignoring the elephant in the living room.