Norman Tsang's son Tyler takes the bus to Staples High School, and almost every day the bus is five to 10 minutes late -- and sometimes more.

Any number of factors can contribute to this, including traffic and how quickly students board the bus. Tsang's son came to expect the bus's tardiness, but then one day the bus arrived five minutes earlier than usual. Unaware, Tyler waited 15 minutes before giving up and turning to his parents for a ride to school. He still missed part of first period.

The anxiety of that day prompted Norman Tsang to create a free app for the iPhone and Android called "Where's Our School Bus?" The simple program allows parents and students to check in when they board or exit a school bus, and this information updates the bus's estimated time of arrival for other students and parents waiting along the bus route.

"We just thought it was a good application that would help a lot of people," Norman Tsang said.

A little research on how to write apps was all that was necessary, said Tsang, a financial investor who developed the app with his wife, Betty, a former teacher at Long Lots Elementary School and Saugatuck Middle School.

"So she's seen (the bus delay problem) from the other side, too," he said.

This is the first app the Tsangs have created. The success of the app depends on crowdsourcing, so when the Tsangs made it available for download, they told friends and neighbors whose children were on the same buses as the Tsangs' children at Staples, Saugatuck and Bedford Middle School.

Word of mouth has helped expand the use of the program, and Norman Tsang said several hundred students and parents now use the app.

Tina Piccolino, who has children at Staples, Bedford and Saugatuck, said "Where's Our School Bus?" has alleviated a lot of anxiety.

"It's been a wonderful tool. It's saved me from driving to school a few times when the bus was late because the app informed me that the bus was on the way just as I was about to drive my son to school," Piccolino said.

The app was made available last November and is still in the beta stage. It has encountered its share of glitches -- including a few times when the app went down -- but it's also evolving as users make suggestions. For example, a message board now allows users to post comments -- perhaps mentioning that a bus is late because of traffic, road work or an accident.

"We wanted to make sure that we got it out and we tested it and made sure that it was working the way we'd like it to work before we have a full, larger release," Norman Tsang said.

Late school buses are not unique to Westport, and Norman Tsang said he envisions other communities adopting the app.

"If it works here, hopefully we can expand and share it with other communities," he said.