WILLIAMSTOWN -- A getting-older thing happened to Michael Adelson on the way to the podium.

As a student at the New England Conservatory, he conducted his friends in their own ensembles. "Then, when my professional career started, I continued to work with people who were about my age," he recalls.

But as he got older, the students seemed to get younger and younger. He went on to become a teacher of conducting and orchestral playing as well as a composer and freelance conductor, with broad experience with student orchestras.

It’s partly that history that brings Adelson to the half-student, half-professional Berkshire Symphony for tonight’s concert. The other connection is the orchestra’s director, Ronald Feldman, who is on sabbatical from Williams College this semester and called on his friend and former cello student to fill in.

Adelson’s program, which begins at 8 in the college’s Chapin Hall, contains three pieces chosen because, Janus-like, they look backward while looking forward. Two contemporary pieces precede Beethoven’s monumental "Eroica" Symphony, No. 3.

How backward and forward?

The finale of the "Eroica," Adelson points out, is based on a theme Beethoven had used before, most prominently in the "Creatures of Prometheus" ballet music. Yet the symphony, vastly larger than any symphony before, "reinvented" the form for later composers, he says.

Keith Fitch’s "In Memory" recalls his composition teacher, Frederick Fox, who died in 2011. Greatly affected by the Newtown, Conn., school shootings, which occurred while he was working on the piece, Fitch subtly quotes from Mahler’s "Songs on the Death of Children" as a subtext to the new work, Adelson says.

Bernard Rands’ "London Serenade" has nothing to do with the city but is a tribute to Edwin London, conductor of the Cleveland Chamber Symphony, on his 60th birthday. Themes from Rands’ early pieces are threaded into the new work.

Fitch’s title page quotes filmmaker Luis Bunuel: "Life without memory is no life at allÅ "

"A nice thought for the concert as a whole," comments Adelson. Both composers are friends of his.

Adelson, 49, grew up in the Detroit area and now lives in Tarrytown, N.Y. His friendship with Feldman goes back to the early 1980s when Adelson was a cello student at Tanglewood and Feldman, then a member of the Boston Symphony, was his teacher.

"He was a very good mentor for me to have, and really helped drive me through those early years of trying to put together a musical life that included a lot of different activities," Adelson said in a telephone interview.

Said Feldman: "I advised him to make new music a cornerstone of his work. He has done just that and has carved a nice place for himself in the music world."

Feldman is spending the semester conducting the Longwood Symphony in Boston, playing chamber music, cleaning house and writing a book on the physical requirements of playing the cello. He and his wife, harpist Elizabeth Morse, also plan some travel.

Adelson, by coincidence, is also writing a book. His is a guide to listeners -- "air conductors," for example -- on how to understand what a conductor actually does and how to come into closer physical contact with the music.

After conservatory studies, Adelson trained with the noted Finnish conducting teacher Jorma Panula. This led to conducting engagements with several Scandinavian orchestras and opera companies. His American orchestral career began with the Los Angeles Philharmonic in 1992.

Among the new-music groups he has led are the Fromm Players at Harvard, who regularly appear at Tanglewood. He also leads young people’s concerts and teaches at workshops and via the Internet.

The current season, however, is mostly a sabbatical from performance. Adelson has taken time off to focus on composing pieces "that had been staring at me expectantly."

There are no premieres scheduled.

"In a way," he says, "that is a good thing because it allows me to do what I need to do with the pieces, and to have the luxury of time to do it. On the other hand, it makes it very tough to actually finish things because you always have the luxury of time to keep changing."

Adelson will be joined by Fitch, the composer, for the final rehearsals and a preconcert talk at 7:15 tonight. Working with students, he finds (as have many others), provides stimulation and enthusiasm for the professional because "you’re experiencing the music alongside people who are experiencing it for the very first time."

Not only that, he says, but you also have more time and latitude to experiment than you would with a professional orchestra, with its more stringent rehearsal requirements.