The internet is a virtual anarchy of information. There is no sense of peer review, which means anyone can publish anything. Critics, seeing that students often plagiarize or accept any information as valid, simply dismiss the internet as a bad idea for education.
The problem with this rejection is that there are great sources out there. Simply handing a kid a textbook and saying "this is the truth" is equally dangerous. According to our textbook, Hawaii offered to become a state and the Spanish-American War occured only after they attacked us first. In reality, we acquired Hawaii through a military coup and we sunk our own ship, the USS Maine, to continue with our own expansionist goals.
So, how do I get students to think critically about the internet? A major part begins with teaching students to find bias by examing sources. On the first day of class, rather than spending the period covering rules and procedures, students do an activity about the dangers of dyhydrogen monoxide (water) and later see the lies from former teachers. Many students have no idea that the George Washington cherry tree story is a lie or that Columbus what not the first European to go to the Americas.
During the actual activity, I have them fill out a chart.
The first row has: Questions
The second row has: Facts
The third row has: Bias of the site - any elements of propaganda
The fourth row has: Reliability: Reason the source is reliable or unreliable
The chart might seem convoluted, but it forces students to ask, "Is this a credible site?" Also, the "in your own words" is key, given the propensity of students to simply copy and paste. Often this had led to some healthy debtates about sources. For example, can we trust either Fox News or CNN? A liberal or conservative will have different views. Should we trust wikipedia? It's often very accurate, but there are many times when someone sabotages a page.