The assignment to design his own museum was all it took for student Christopher Thach to start imagining.

The 17-year-old high school senior at Carver High School for Engineering and Science in Philadelphia envisioned a cavelike sphere with rooftop spikes jutting toward the sky and aurora lights to make the building glow.

That the design would have to adhere to real-life engineering, structural, and land-use guidelines in its hypothetical place on the Benjamin Franklin Parkway wasn't important - yet.

This was the time for no boundaries, said architect William McDowell, of the Barnes Foundation museum.

"Dream," McDowell told Thach and his fellow students.

The assignment to design the imaginary Envision Peace museum is the latest project for a group of 22 teenagers taking part in the ACE Mentor Program, a 15-year-old initiative to introduce students to careers in architecture, construction, and engineering (ACE).

The program, which has an expected enrollment this year of 250 students in the five-county Philadelphia area, offers teenagers the chance to learn from industry professionals, working alongside them in internships, visiting job sites, and designing buildings based on the real-life specs of those going up in the region.

Over the years, students have worked with volunteer mentors to design their versions of a new dormitory for the University of Pennsylvania, a house for Habitat for Humanity, and retail space at the Comcast Center.

"We tell them to go after the job" as if they were professionals, said Diana Eidenshink, ACE's Northeast regional director - whose father, Charles Thornton, an engineer, cofounded the mentorship program in 1995 to increase diversity in the building trades.

"They work as a team and do the drawings. They put together the ideas about what the building looks like and how much it will cost."

Students then often make their own presentations before the building owners.

This year, many of the participants will take the specs of Philly Live! - a restaurant and entertainment complex slated to be built on the site of the Spectrum in South Philadelphia - and design their own version.

They'll also go on field trips to the trade unions to learn about such aspects as laying bricks and construction-site safety.

According to a 2010 ACE study, 66 percent of the program's 50,000 alumni nationally are either studying architecture, engineering, construction, and the skilled trades, or are already working in one of those fields.

Of this region's students, recommended to the program by their school counselors, about 180 this year will be from the city and 70 from the suburbs. The students are divided into teams that meet after school once every other week.

Kris Wint, a supervisor of education development at Haines & Kibblehouse construction firm in Skippack, leads a team based at Souderton Area High School in Montgomery County that starts meeting this week to design a high school building. They'll enter the project in a national competition cosponsored by the Construction Industry Roundtable and the ACE program.

Last year, the group designed a version of the Penn dorm in the shape of an X.

"A lot of us have been visiting dorms at colleges, and they're just squares," said Jeremy Ross, 17, an ACE program student and Souderton senior. "The X is kind of cool and allowed us to use our creativity."

In New Jersey, ACE officials are developing a plan for a team of about 20 students they expect to start soon at MetEast High School in Camden.

The students working with the Barnes Foundation are part of a special two-year work-study program for which the ACE program received a $250,000 government grant. In addition to the design curriculum during the school year, the students also work in paid summer internships at architecture, engineering, and construction firms.

The Barnes program has included a visit to the foundation's current location in Lower Merion, along with discussions about its founder, Albert Barnes; the museum's history; and the controversy surrounding the collection's move to the Parkway.

McDowell anticipates that the exercise of designing a museum under the guidance of professionals working with the Barnes will leave a mark on the students.

"Hopefully," the architect said, "they'll come back to Philadelphia after their college careers and think big and do great things."

Carver student Trevaughn Tummings, 17, lives in Wynnefield, not far from the museum's Lower Merion location, and had never heard of the Barnes. When she visited the museum earlier this year, her first thought was, "Wow, this guy was rich."

Tummings plans to be a civil and environmental engineer with a focus on green design, because, she said, "the last drip of oil will be, like, tomorrow."

Nicole Golden, 17, of Constitution High School, spent her summer internship at L.F. Driscoll Co. L.L.C., a construction-management firm based in Bala Cynwyd. She sat in on meetings involving an expansion of the Hospital of the University of Pennsylvania and learned to read blueprints.

Tummings doesn't yet have a design idea for her museum, but she's thinking oddball, to stand out from the conventional.

"The buildings in Philadelphia are nice, but they're a bunch of 90-degree angles," Tummings said. "I want mine to be weird."

Contact staff writer Kristin E. Holmes at 610-313-8211