The evidence mounts. We’re learning why so much preaching and teaching produces thin results in the lives of the recipients.

It’s not due to the speaker’s lack of charisma, or failure to prepare, or theological imprecision.

It’s not due to the irrelevance of the message itself. It’s as relevant as ever.

Rather, it’s due to how our brains are wired. Much of the the typical 20- to 40-minute lecture-style monologue never makes it to the brain–or the heart. So, much of the finely prepared and delivered teaching falls, quite literally, on deaf ears.

Educators have been studying this phenomenon for some time now. Some of the latest research comes from the University of Rochester. Research scientist Philip Guo recently studied the efficacy of online education, specifically the use of teaching videos. He found that the average engagement time with any teaching video maxes out at 6 minutes, regardless of the video’s total length. And engagement times actually decrease the longer the video. For example, students typically spend only 3 minutes on videos that are 12 minutes or longer.

The research on teaching videos may also be applicable to live in-person teaching as well. British researchers recently found that the average adult attention span has dropped from 12 minutes a decade ago to just 5 minutes now. That means if a preacher or teacher speaks for 30 minutes, the audience will tune out 84 percent of the message.

Personal spoiler alert. I find this data backed up–in my own personal attention span experience. I’m afraid it’s true for me. After 5 or 6 minutes of a sermon, lecture or speech, my mind wanders. I’m thinking about other stuff. (The time is not totally wasted. I often do some of my best thinking while someone talks into a microphone in the background.)

Everybody knows children have short attention spans. They telegraph their disconnection with the teacher. They squirm, rustle, vocalize and act up when their minds wander. Adults disconnect too. They’re simply better at concealing their mind-wandering. They may look directly at the speaker, and even nod, but after a few minutes, their minds have left the building.

They’re not being impudent or uncaring. They’re simply following their brains’ limited ability to lock on to a speaker for a length of time.

How can teachers and preachers adapt to this reality of the short attention span? Researcher Guo said, “The take-home message for instructors is that, to maximize student engagement, they should break up their lectures into small, bite-sized pieces.” So, effective teachers and preachers will set up a thought for a few minutes, then switch to different points of attention. These may include another person–a different speaker or an interviewee. Or, perhaps a video clip, or a simple experience, or a prompted discussion or conversation. Every few minutes they change the mode, renew everyone’s attention, return to another short bit of lecture, and so on.

We see evidence that Jesus understood the limits of the human brain. Most of his recorded teachings are short, succinct–and powerful. And he even acknowledged the limited capacity of his listeners when he said, “I have many more things to say to you, but they are too much for you now.” (John 16:12)