Sources:

1) An email we received on March 9, 2019 from Alan Shaw, who was the drummer in the first lineup of 'The Misfits':

Glad to have found your site. I can help fill-in-the-blanks on The Misfits.
I attended Castle Heights Military Academy in Lebanon, TN. In the fall of 1961, Duane was playing practice sessions in this room with John "Tex" Lanier, from Austin, Texas. It wasn't long before the word got out about their talent, I joined in playing drums on an old snare I had retrieved from the school's band locker in the auditorium. It wasn't long before I had piece-mealed a drum kit of sorts comprised of a snare, one tom-tom, a bass drum, and two cymbals... a ride and a crash.
Dave Johnson, from Lafayette, Tennessee soon joined in playing tenor sax. The last member to join was Pat O'Quinn, New Iberia, Louisiana who played rhythm guitar.
Duane and I shared co-founder status and we began holding practice sessions in the school auditorium. At that time Duane and Tex both played "Strats" and O'Quinn played a "Les Paul". During the Christmas break, Duane acquired a Cherry Red Rickenbacker, which I believe he slept with.
We named the band "The Misfits" because we felt like we were just that.
During the rest of the year, we played at school dances and off-campus sites as well. We didn't have a singer, so we each took turns at providing vocals. Each one of us had one or two songs we could limp through. We mostly played instrumentals and our anthem was a rowdy "Frat" song outta Alabama known as "Hell Yes (Yeah)", which we played until exhaustion overtook us. We called our style "Marathon Music" because it was just that. Often times during these renditions Johnson would develop a nose bleed from extended and continuous playing and he'd have to sit out until he could stem the flow of blood.
Years later I understood the penchant the Allman Brothers had for marathon music.
I graduated that year, but the band continued with Gregg joining in 1962-1963. He mentions the band in his memoirs written many years later.

You'll have to take my word for most of what I've written here...but I have included a copy of an inscription by Duane in my CHMA yearbook, The Adjutant, as proof of my membership in the band.
Thanks and Good Luck
Alan Shaw
Original Drummer
The Misfits
 

(click to enlarge)

On March 27, 2019 we received additional information from Alan Shaw:

Duane was enrolled at CHMA in the fall of 1961. He remained at Heights that entire year. I know this to be a fact 'cause I was there. You will note that Duane inscribed my '62 yearbook. Yearbooks are not released until late spring. That would've been 1962.
I believe that Gregg entered Heights in the fall of 1962? But, that could be open to conjecture? However, I can attest to the fact that Gregg was definitely NOT at Heights in the spring of '62, but he was there for the fall semester of 1962. Duane and Gregg were both going to CHMA at the sime time, from the Fall of '62 through the Spring of '63. Gregg was in another version of The Misfits when I had already left CHMA. He wasn't there until the Fall of 1962 at the earliest.

As I already mentioned, the band's membership, when Duane and I formed The Misfits, consisted of Duane and me. Then there was "Tex" Lanier, who shared lead guitar with Duane, Dave Johnson was on sax, and Pat O'Quinn played rhythm guitar. We didn't have a bass player.

This article from the Castle Heights Military Academy school paper "The Cavalier" was posted by Alan Shaw on the Facebook group page of the Castle Heights Military Academy:

2) Scott Freeman: 'Midnight Riders - The Story Of The Allman Brothers Band', page 11 (Little, Brown & Company, 1995):

By the ninth grade, Duane had lost all interest in school - "the fever" was becoming all that mattered. He dropped out the next year, and, in a last-ditch effort to make sure that Gregg didn't follow in his big brother's footsteps, Geraldine send Gregg back to Tennessee to Castle Heights for his sophomore year in 1962. "My mother decided to send me back there because we were running wild and playing music and our grades were biting the dust," Gregg said.


3) Randy Poe: 'Skydog - The Duane Allman Story', page 10 (Backbeat Books, 2006):

But soon the guitar became an obsession for Duane, having such an effect on his schoolwork that he found himself being sent back to Castle Heights. Although Gregg would eventually graduate from Daytona Beach’s Seabreeze High School in 1965, both of the brothers bounced in and out of CHMA between 1961 and 1964. Duane’s eventual departure from formal education wasn’t a matter of his deciding to leave on a specific day, never to return. He had simply lost interest in going to school with any regularity once he discovered the guitar. For at least a few months in the latter part of 1963, Duane and Gregg were both going to CHMA at the same time.


4) Gregg Allman: 'My Cross To Bear', page 36 (William Morrow / Harper Collins Publishers, 2012):

Then my mother came to me around mid-August and said, “Your grades are so bad, you’re going back to military school.” I was crushed. Just as I was preparing to leave, I found out that the school was full. My brother could get in, but I couldn’t go until January. My brother’s grades didn’t get him in as a junior, though, but as a sophomore. Pissed him off, man. He was back in little brother’s grade, back with the hired help, so to speak.
Believe me, it wasn’t because he didn’t know the shit. He could learn it just like that. It was just that now he had a guitar under his arm constantly. He was learning that guitar, but they didn’t notice things like that. No grades for that—not back then, anyway. So Vicky and I stayed together that fall, and right around Christmas I got the news that I was going back to Castle Heights in January with my brother.


5) Galadrielle Allman: 'Please Be With Me: A Song For My Father, Duane Allman', page 51 (Spiegel & Grau, 2014):

In 1962, when Gregg was a sophomore and Duane should have been a junior, she decided to send them both back to Castle Heights Military Academy. Duane had missed so much school that Jerry hired a special tutor so he could pass the entrance exam, but he was still held back and enrolled as a sophomore, a further indignity.


6) http://www.wilsonpost.com/style/32/9910-gregg-allman-lets-it-all-hang-out

...Besides those topics, Allman explores his six marriages (including his three years with pop star Cher), substance abuse, the “cursed band” and its many breakups, and his years as a student at Lebanon’s Castle Heights Military Academy.
While he disses Heights for the most part, it was at here that the brothers formed one of their earliest bands, The Misfits.
“We played there at the school at dances after football games. They’d bring girls in from town, and we would play for those dances, and they let us wear civilian clothes. That was a real treat for us,” Allman said during a phone interview Friday...