(CBS News) Fethullah Gulen is the Turkish Islamic cleric at the center of a popular and growing movement, with millions of disciples who follow his teachings of tolerance, interfaith dialogue, and education. Some have even started a chain of successful charter schools here in the U.S., with an emphasis on math and science. Yet Gulen himself remains shrouded in mystery. Lesley Stahl travels from Turkey to Texas to report on how the movement is spreading, and on the man behind it all.

The following script is from "The Gulen Movement" which aired on May 13, 2012. Lesley Stahl is the correspondent. Shachar Bar-On, producer.

Over the past decade scores of charter schools have popped up all over the U.S., all sharing some common features. Most of them are high-achieving academically, they stress math and science, and one more thing: they're founded and largely run by immigrants from Turkey who are carrying out the teachings of a Turkish Islamic cleric: Fethullah Gulen.

He's the spiritual leader of a growing and increasingly influential force in the Muslim world -- known as "The Gulen Movement" -- with millions upon millions of disciples who compare him to Ghandi and Martin Luther King. Gulen promotes tolerance, interfaith dialog, and above-all: he promotes education. And yet he's a mystery man -- he's never seen or heard in public -- and the more power he gains, the more questions are raised about his motives and the schools.

[Lesley Stahl: Hi everyone.

Students: Hi.]

This is the Harmony School in Houston, part of a rapidly expanding chain of 36 charter schools in Texas. They serve mostly underprivileged students and they all emphasize math and science.

[Student: Inside there is an elastic collision between the gas particles.

Student: What this is is a static electricity generator?]

Class work stresses hands-on experiments and competitiveness. Students made this hovercraft out of leaf-blowers for a science contest.

[Lesley Stahl: It's great!]

Being a charter chain means these are public schools, costing tax payers nearly $150 million a year.

[Lesley Stahl: So you don't even have a drivers' license yet?

Student: But I have a robotics license!]

Julie Norton is an administrator with the Harmony chain of schools.

Julie Norton: So we have about 20,000 students.

Lesley Stahl: Is there a waiting list?

Julie Norton: Yes, we have a waiting list. We have approximately 30,000 students on our waiting list. We have more students on the waiting list than we have enrolled in the schools.

The education here gets high marks, as students get state-of-the-art technology and extensive one-on-one tutoring.

[Lesley Stahl: Do you get excited to come to school?

Student: Yea I wake up like whooo.]

The enthusiasm is hard to miss, as is the fact that many of the teachers are Turkish, some just recently arrived and hard to understand.

[Lesley Stahl: When did you get here, to the United States?

Teacher: (unintelligible)]