The article both states that the device would allow teens to be tracked after they left school, and that the chips are read by electronic readers located throughout the campus. I don't see how both can be true. If you need electronic readers to read the chips, then they are going to work once a teen is out of range.
I'm surprised by the responses here. I'm curious how many of the posters have kids who attend schools with thousands of students, or have recently visited a campus of this size.
As Queen of the Meadow pointed out, all a kid has to do is take it off for it to not work. Although badges being worn front and center is the rule at high schools here -- anyone on campus not wearing a badge is stopped. None the less, finding one's child when they aren't opposed to being found is actually something most parents want. Actually, being able to find our children at ALL times is a pretty basic thing to most parents. I don't know many parents, even of teens, who have a "if they show up, great, if not, don't worry" attitude.
Personally, I would like a system that timestamped when each child entered campus and left campus. One of my teens was late getting home from school, and when I started to backtrack to figure out at what time she went missing, the school didn't know. It ended up that she was on a field trip that was an hour late getting back, but the office didn't have a clue where she was or any way to figure it out. They had that she arrived at school that morning, then nothing. The school we are considering switching to does attendance every hour and has an automatic system to email parents at the end of the school day with any unexcused absences. They also have 3 students out of regular class each hour of the day to act as runners to go find students who need to be found (for things like dentist appointments and what not). With thousands of students and a huge campus, this is a big job.
Because of cell phones, kids are easier to find OUT of school than in. They aren't allowed to use their cell phones at schools. Many schools don't even allow kids to have their cell phones on them.