I'm not exactly sure when my mother started singing in the Tanglewood Festival Chorus (it was formed in 1970--she might have been one of the charter members), but I do know that it was somewhere between the time that she had to stop playing the flute and the time that I started playing the flute.
I became aware of my mother's participation in the Chorus when I was in the 7th grade. I used to see her music on the piano, and was particularly struck by the motet Jesu, meine Freude, BWV 227. I discovered that I could sing the alto part and play the other vocal parts, thereby hearing how all the voices worked together.
I guess my mother figured I was interested in choral singing, so in September of my 8th-grade-year, she brought me to a rehearsal. We sightread two-chorus music by Gabrielli and Schütz and music by Stravinsky (the Symphony of Psalms and the Canticum Sacrum). I had a short audition for John Oliver, the director of the chorus, where I sang a bit of the Canticum Sacrum. I had no idea it was hard: the excitement of the evening etched the tone rows in my spongy and fearless adolescent brain, and I was thrilled that he let me join the chorus as its youngest member.
We took part in one of the "Spectrum Concerts" in Symphony Hall during the regular season. The program, conducted by Michael Tilson Thomas, was Venetian: Gabrielli and Schütz motets with antiphonal brass playing from the Symphony Hall Balconies, the Stravinsky Symphony of Psalms, and the Canticum Sacrum, which Michael Tilson Thomas always called the "Canticum Gesundheit." I still can't figure out why he called it that.
The summer season included a Friday evening "Weekend Prelude" in the Tanglewood Shed. We sang the Bach motet Komm, Jesu, komm, some Brahms motets, and some choral pieces by Hugo Wolf. We also got to sing the Haydn Creation.
I loved that summer. Because of my experience in the chorus, I decided that I wanted to be a singer. I asked Phyllis Curtin, the person who I most admired as a voice teacher, when I could start studying. She told me that at 14 I was too young to train my voice. She advised me to play the flute and start studying voice when I was a bit older. So I started playing the flute, and I fell in love with playing the flute. My vocal aspirations fell deep into the background, and ultimately vanished, and I threw myself, body and soul, into playing the flute.
The next Tanglewood season had music that John Oliver (correctly) determined was too heavy for my voice, especially if I had any interest in developing it (they were doing Mahler 8 and Beethoven 9), so I didn't sing in the chorus the next year. I discovered the Fromm Festival the next summer, and decided that I was doing the right thing by playing the flute because I could play lots of contemporary music. My 15-year-old reasoning told me that nothing atonal could really sound bad on the flute as long as it is played with a beautiful sound. I also started hanging out with composers that summer, and I decided that if tonality ever came back in style I would start to write music. It took another decade or two, but it was finally acceptable for people who wrote new music to use something other than atonal material and to organize it in a way that wasn't serial.