Kik Messenger also allows unlimited texting for free and effectively offers anonymity to users.
As with anything online, each of these services comes with caveats.
Snapchat acknowledges on its website that messages aren't guaranteed to disappear: Anyone receiving a text or photo can within 10 seconds capture a "screenshot," taking a photo of their device's screen, and save that image. Video also can be downloaded, although Snapchat says it alerts senders when material is saved.
Instagram is considered tame as long as kids adjust their privacy settings to limit who can see their photos and don't post nudity, which could subject them to child pornography laws. But Levey said many parents don't know their kids are using Instagram until there's trouble - usually when kids post inappropriate photos at parties and these begin to circulate among their social circles.
Parents often hand their kids a mobile device without understanding exactly what it can do, said Dale Harkness, a technology director at Richmond-Burton Community High School in Richmond, Ill. He estimates that even without using social media services, the average high school student probably transmits some 150 texts a day.
"It's not anything that every parent and grandparent hasn't already seen," Harkness said. The problem, he adds, is that actions "get documented, replayed and sent around." He said that students "forget how fast it moves and how far it goes."
That was the case at Ridgewood High School in Ridgewood, N.J., where a male student allegedly took a screenshot of nude pictures sent to him by female classmates via Snapchat, then posted the pictures on Instagram. According to a letter to parents by the school district's superintendent that was later posted online, police warned students to delete any downloaded pictures or face criminal charges under child pornography laws.