So far, only 40 Rikkyo fourth graders have the tags, but all 718 students are expected to carry them by the end of October.
The tags contain tiny computer chips linked to small antennae. Radio-wave transmitters near the school's front gate read the chips, which have unique signals for each student. Antennae send information _ the exact times and the frequency with which the children enter and exit _ to a computer that e-mails the data to parents' mobile phones.
Fujitsu's Koichi Yamakawa said the system is designed to read as many as 100 students' tags simultaneously.
The system will eventually serve another purpose: Anyone entering the gates without a tag will trigger an alarm.
Rikkyo officials say the tags aren't cheap. Fujitsu is charging the school 15 million yen ($136,000), which includes the 3,500-yen ($31.80) per-tag cost. But Tanaka, Rikkyo's headmaster, says it's worth the expense.
"The school has to do all it can to ensure the safety of the children,'' he said.